WO2000013154A2

WO2000013154A2 - Electronic curfew monitoring system

Info

Publication number: WO2000013154A2
Application number: PCT/CA1999/000792
Authority: WO
Inventors: Douglas Hayward Blakeway; Steven Laurence Rosset
Original assignee: Strategic Technologies Inc.
Priority date: 1998-08-28
Filing date: 1999-08-30
Publication date: 2000-03-09
Also published as: AU5403899A; WO2000013154A3; CA2246022A1

Abstract

A method, apparatus, and system for remotely monitoring the location of a monitoree within a monitored area. The method includes the steps of: securing to a monitoree by a harness a closeable housing containing a transmitter for transmitting an identification signal for identifying the transmitter; locating within a monitored area a receiver for receiving the identification signal; measuring the signal strength of the identification signal received at the receiver; and comparing the signal strength to a predetermined signal strength threshold to determine whether the transmitter is located within the monitored area.

Description

ELECTRONIC CURFEW MONITORING SYSTEM

FIELD OF THE INVENTION

The present invention relates to systems for determining whether an entity is presently located inside or outside a predetermined area. More particularly, the invention relates to electronic curfew monitoring systems used by the State to monitor a person's presence in or absence from a particular location.

BACKGROUND OF THE INVENTION An electronic curfew monitoring system enables the State to monitor an individual's presence in or absence from a particular location. For example, an individual might be confined to his home during non-business hours. This arrangement permits the State to control an individual's interaction with society. At the same time, the arrangement allows the individual to avoid the brutality of prison and gives him the opportunity to earn a wage and participate in a counseling or rehabilitation program.

Although less forbidding than prison, an electronic curfew monitoring system must nevertheless be implemented carefully to ensure that containment is secure and resistant to tampering. Generally, an electronic curfew monitoring system includes a transmitter secured to the monitoree and a receiver located near the centre of the monitored area.

The transmitter regularly transmits an identification signal to the receiver to confirm that the transmitter, and hence monitoree, is located within the monitored area. In turn, the receiver periodically transmits a status message to a central monitoring computer administered by the State or a security monitoring company over a pre-arranged communication channel, for example the public switched telephone network.

However, should the receiver not receive the identification signal for a predetermined period of time, then the transmitter, and hence the monitored individual, has likely moved outside of the monitored area. In response, the receiver transmits an escape signal to the central monitoring computer over the pre-arranged communication channel.

Conventional electronic curfew monitoring systems have a number of vulnerabilities. For example, it is a fundamental assumption that the location of the transmitter corresponds to the location of the monitoree. However, a monitoree may successfully remove the transmitter from his person, leaving it within the monitored area while he strays.

Alternatively, the monitoree may try to stray undetected by bringing the receiver with him. So long as he provides a conventional receiver with sufficient operating power and a suitable alternate communication channel, perhaps through a cellular telephone, he can succeed.

A further problem with conventional systems is that they detect that a monitoree is either inside or outside of the monitored area but not that he is moving toward or beyond the perimeter of the monitored area. In other words, they detect a completed escape or intrusion but not an escape or intrusion in progress.

Another problem with conventional systems is that they are difficult to install. Generally, the transmitter is placed at the perimeter of the monitored area and the receiver's signal path is attenuated until the receiver no longer detects the identification signal from the transmitter. Such signal attenuation is clearly disadvantageous because it hinders the receiver's ability to decode the identification signal.

However, a further problem with this installation method is that the interaction between the identification signal and the monitored area is complicated. There will likely be transmitter locations outside of the monitored area perimeter that will permit the identification signal to be received at the receiver. Similarly, there will likely be transmitter locations within the monitored area perimeter that will prevent the identification signal to be received at the receiver. With conventional systems, there exists no easy way for the installer determine and then compensate for such interactions.

A related problem with conventional systems is that there may be transmitter locations within the monitored area from which a first identification signal will not reach the receiver but from which a different identification signal would reach the receiver. In other words, null or dead spots within the monitored area depend on the nature of the identification signal.

What is needed is an electronic curfew monitoring system directed to these problems.

BRIEF SUMMARY OF THE INVENTION

Aspects of the invention are embodied in a method, apparatus, and system for remotely monitoring the location of a monitoree within a monitored area.

According to a first embodiment, there is provided a method including: securing to a monitoree by a harness a closeable housing containing a transmitter for transmitting an identification signal for identifying the transmitter; locating within a monitored area a receiver for receiving the identification signal; measuring the signal strength of the identification signal received at the receiver; and comparing the signal strength to a predetermined signal strength threshold to determine whether the transmitter is located within the monitored area.

The method might also include at the receiver periodically logging data into a data log, wherein logging data in a data log includes logging at least one of: the signal strength, data describing the state of the receiver, data describing the state of the closeable housing, and data describing the state of the harness. Furthermore, the method might include at the receiver periodically uploading the data log to a server.

Desirably, the method includes: detecting whether the receiver has been moved, connecting the receiver to receive power from electrical power mains and detecting when the receiver has been disconnected from the electrical power mains, and connecting the receiver to a communication channel to the server and detecting when the receiver has been disconnected from the communication channel. Additionally, the method includes generating an alarm signal if within a predetermined time interval the receiver has been both moved and disconnected from either the electrical power mains or the telecommunication channel.

Preferably, the method includes detecting whether the closeable housing has been at least partially opened and encoding within the identification signal an indicia that the closeable housing has been at least partially opened. Thus, the step of securing to a monitoree might include: forming the harness into a loop having first and second ends, placing a limb of the monitoree through the loop, and securing the first and second ends of the loop within the closeable housing.

Similarly, the method might further include: detecting whether the harness has been modified and encoding within the identification signal an indicia that the harness has been modified. In this situation, detecting whether the harness has been modified includes detecting whether the harness has been cut or stretched whether an electrical jumper has been connected to the harness.

The method might further include calibrating the predetermined signal strength threshold, for example by selecting one of a set of preset values or by first locating the transmitter at a boundary of the monitored area and then setting the predetermined signal strength threshold equal to the signal strength or the signal strength multiplied by a scaling factor. By extension, one might calibrate a set of predetermined signal strength thresholds by: locating the transmitter at successive distances from the receiver, and setting members of the set of predetermined signal strength thresholds equal to the signal strengths corresponding to the locating the transmitter at respective successive distances from the receiver.

According to another embodiment of the invention, there is provided an apparatus having: a transmitter for transmitting an identification signal, a closeable housing enclosing the transmitter, the housing having first and second opposite ends, and an elongated and electrically conductive harness having first and second ends, the first and second ends being transversely receivable into the first end of the housing for engagement by the housing and electrical connection to the transmitter when the housing is in a closed state, whereby the harness is configurable into a loop for securing the housing.

The apparatus might further include: a harness-tamper voltage detector for detecting a potential difference between the first and second ends of the harness, and a harness-tamper signal generator for generating a harness- tamper signal in response to the harness-tamper voltage detector detecting a change in potential difference greater than a predetermined threshold.

Additionally, the first end of the harness might support a perpendicular spur, the spur being receivable into the second end of the housing for engagement by the housing and electrical connection to the transmitter when the housing is in the closed state. In this case, the apparatus might further include: a housing- open voltage detector for detecting a potential difference between the first end and the spur of the harness, and a housing-open signal generator for generating a housing-open signal in response to the housing-open voltage detector detecting a change in potential difference greater than a predetermined threshold.

Desirably, the apparatus also includes a lock-bolt receivable into the closeable housing to secure the closeable housing in the closed state. For further security, the apparatus might include a key receivable into the lock-bolt and the first end of the harness to secure the lock-bolt to the first end of the harness, whereby the lock-bolt cannot be removed from the housing while secured to the first end of the harness. The lock-bolt and the key might further include cooperating members for securing the key to the lock-bolt. In particularly, the cooperating members on the key might include a broad head and a catch. Desirably, the key further includes a breakaway joint located between the broad head and the catch such that the broad head is separable from the catch, whereby the key may be removed from the lock-bolt and the first end of the harness.

According to yet another embodiment of the invention, there is provided an apparatus including a receiver for receiving an identification signal transmitted by a transmitter, the receiver having: a signal strength detector for detecting the strength of the identification signal received at the receiver, and a comparator for comparing the signal strength to a predetermined signal strength threshold to determine whether the transmitter is located within a predetermined monitored area.

The apparatus might further include a motion detector for generating a motion signal when the apparatus has moved.

Desirably, the apparatus includes: a power connector for connecting the apparatus to receive power from electrical power mains, and an electricity detector for generating a disconnection signal when the apparatus has been disconnected from the electrical power mains. Similarly, the apparatus might include: a communication connector for connecting the apparatus to a communication channel, and a channel detector for generating a disconnection signal when the apparatus has been disconnected from the communication channel. Thus the apparatus might include including an alarm for generating an alarm condition when the apparatus has been both moved and disconnected from either the electrical power mains or the communication channel within a predetermined time interval.

Preferably, the apparatus further including a data-logger for periodically logging in a data log at least one of: the signal strength, the motion signal, and the disconnection signal.

Advantageously, the comparator might be adapted to compare the signal strength to a set of predetermined signal strength thresholds to determine whether the transmitter is located within one of a set of predetermined monitored areas.

Finally, according to still another embodiment of the invention, there is provided a system including: the apparatus described as the second embodiment, and the apparatus described as the third embodiment, wherein the apparatus described as the third embodiment is the transmitter transmitting the identification signal to the receiver for receiving an identification signal transmitted by a transmitter as described in the second embodiment.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING These and other features, aspects and advantages of the invention may be understood with reference to the following claims, description, and accompanying drawings, in which,

Figure 1 is a perspective view of an electronic curfew monitoring system according to a first embodiment of the invention, showing both a base station and a remote station including a harness; Figure 2 is a longitudinal view of a section of the harness according to the first embodiment of the invention; Figure 3 is a perspective view of the harness in a looped configuration according to the first embodiment of the invention;

Figure 4 is a perspective view of a baseplate in the remote station according to the first embodiment of the invention; Figure 5 is a perspective view of a coverplate in the remote station according to the first embodiment of the invention; Figure 6A is a cross-sectional view showing the alignment between a portion of the coverplate and a portion of the harness according to the first embodiment of the invention;

Figure 6B is a cross-sectional view showing the connection between a portion of the coverplate and a portion of the harness according to the first embodiment of the invention; Figure 7 is a perspective view of a locking-bolt in the remote station according to the first embodiment of the invention;

Figure 8 is a perspective view of a key in the remote station according to the first embodiment of the invention; Figure 9 is a block diagram of remote circuit module in the remote station according to the first embodiment of the invention, the remote circuit module including a remote microprocessor and remote

ROM; Figure 10 is a block diagram of a base circuit module in the base station according to the first embodiment of the invention, the base circuit module including a base microprocessor and base ROM; Figure 11 is a flowchart diagram of a REMOTE MAIN LOOP routine stored in the remote ROM for programming the remote microprocessor according to the first embodiment of the invention;

Figure 12 is a flowchart diagram of an INTERRUPT routine stored in the remote ROM for programming the remote microprocessor according to the first embodiment of the invention;

Figure 13 is a flowchart diagram of a BASE MAIN LOOP routine stored in the base ROM for programming the base microprocessor according to the first embodiment of the invention;

Figure 14 is a flowchart diagram of a TIMER CONTROL routine stored in the base ROM for programming the base microprocessor according to the first embodiment of the invention; Figure 15 is a flowchart diagram of a RECEIVER CONTROL routine stored in the base ROM for programming the base microprocessor according to the first embodiment of the invention;

Figure 16 is a flowchart diagram of a SETUP RANGES routine stored in the base ROM for programming the base microprocessor according to the first embodiment of the invention;

Figure 17 is a flowchart diagram of a PREDEFINED RANGE routine stored in the base ROM for programming the base microprocessor according to the first embodiment of the invention; Figure 18 is a flowchart diagram of a CALIBRATE RANGE routine stored in the base ROM for programming the base microprocessor according to the first embodiment of the invention;

Figure 19 is a flowchart diagram of a PROGRESSIVE RANGES routine stored in the base ROM for programming the base microprocessor according to the first embodiment of the invention;

Figure 20 is a flowchart diagram of a LOCATE TRANSMITTER routine stored in the base ROM for programming the base microprocessor according to the first embodiment of the invention; and

Figure 21 is a flowchart diagram of a DETECT TAMPERING routine stored in the base ROM for programming the base microprocessor according to the first embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The Major System Components

Referring to Figure 1 , an electronic curfew monitoring system according to a first embodiment of the invention is shown generally at 10. The curfew monitoring system 10 includes a base station 12 and a remote station 14.

Referring briefly to Figures 1 and 10, the base station 12 contains a base circuit module 16 which includes a keypad 18 for receiving input from an operator, a visual display 20 for presenting information to the operator, and a radio frequency receiver 22 for receiving signals from the remote station 14. The base circuit module 16 further includes a power input 24 for connection to an electrical power main 26 and a communication line 28 for connection to a communications circuit, in this embodiment a public switched telephone network 30.

Referring briefly to Figures 1 and 9, the remote station 14 includes a remote station housing assembly 32 which contains a remote circuit module 34 having a radio frequency transmitter 36 for transmitting signals to the radio frequency receiver 22 in the base station 12. A harness 38 is releasably attached to the remote station housing assembly 32 and forms a loop defining an aperture 40 for receiving and securing the arm or leg of a monitoree whose location is to be monitored.

The remote station housing assembly 32 further includes a baseplate 60 and a cooperating coverplate 58. The baseplate 60 and the coverplate 58 interlock to capture the harness 38, with the baseplate 60 being circumscribed by the harness 38 and the coverplate 58 being located outside of the harness aperture 40. The remote circuit module 34 is encased with the coverplate 58.

The Harness

Referring to Figures 2 a portion of the harness 38 is illustrated in longitudinal section in a non-looped, or linear, configuration. The linear configuration is the natural state for the harness 38 before use.

The harness 38 includes a substantially L-shaped substrate 42. At the horizontal of the "L", the substrate 42 defines a first set of registration holes 44. Along the vertical of the "L", the substrate 42 defines a second set of registration holes 46. At the horizontal tip of the "L", the substrate 42 defines a first keyhole 48 having a substantially circular cross-section augmented by a first pair of opposing notches 47. As will be described below, the first and second sets of registration holes 44, 46, and the first keyhole 48 engage various portions of the remote station housing assembly 32.

The substrate 42 also defines a conductor channel 52. The harness 38 further includes a conductive strip 54, which cooperates with the conductor channel 52 to be accepted and retained therein. The conductor channel 52 and the conductive strip 54 extend along the substrate 42, along both the vertical and the horizontal portions of the "L". The conductive strip 54 has sufficient resistivity such that when an electrical current is passed through the conductive strip 54, a potential difference is easily measured between different points along the conductive strip 54.

Although the conductive strip 54 may be sealed within a unitary substrate 42 of moderate strength and hardness, it has been found desirable to manufacture the substrate 42 from a strong, tough substance, in this embodiment nylon, and to seal the conductive strip 54 and the substrate 42 within a softer and more flexible surface shell 55 which does not plug or otherwise deform the first and second sets of registration holes 44, 46 or the first keyhole 48. In this embodiment, the substrate 42 acts as a reinforcing strip within the softer surface shell 55 of the harness 38.

A short distance away from the horizontal along the vertical of the "L", the substrate 42 defines a strain-relief notch 50, which is the structurally weakest point of the substrate 42. The size and shape of the strain-relief notch 50 may be selected to tune the tensile strength of substrate 42.

The substrate 42 further defines a set of wells 56, which pass through the bed of the conductor channel 52 toward the conductive strip 54. As will be described further below, the wells 56 enable various portions of the remote station housing assembly 32 to pass through the tough substrate 42 which would otherwise prove difficult. Refer ng now to Figure 3, the harness 38 is illustrated in its looped configuration for engaging the remote station housing assembly 32.

Referring briefly to Figure 6, the exterior surface of that portion of the harness surface shell 55 adjacent the conductive strip 54 desirably defines a set of counterbores 57. As will be described further below, some counterbores in the set of counterbores 57 engage various portions of the remote station housing assembly 32.

The Remote Station Housing Assembly: The Baseplate

Referring now to Figure 4, the baseplate 60 is described in greater detail. The baseplate 60 includes a base 62 substantially bounded by first, second, third, and fourth base walls 64, 66, 68, 70.

The first and third base walls 64, 68 define between them a first base notch generally illustrated at 72. Similarly, the second and third base walls 66, 68 define between them a second base notch generally illustrated at 74. The first and second base notches 72, 74 are sized to cooperate with the harness 38 in its loop configuration to receive the harness 38 in a transverse orientation.

A first base registration post assembly 76 extends from the base 62 proximate to the first base notch 72, the first base registration post assembly including first, second and third base registration posts 76a, 76b, 76c. Similarly, a second base registration post assembly 78 extends from the base 62 proximate to the second base notch 74. The first and second base registration post assemblies 76, 78 respectively cooperate with the first and second sets of registration holes 44, 46 to precisely engage the harness 38 in a transverse loop orientation to the base 60.

It will be noted that at any one time, the second base registration post assembly

78 can engage but one member of the second set of registration hoies 46. In this way, provision is made for a harness 38 having an aperture 40 with a selectable diameter.

The first and fourth base walls 64, 70 define between them a third base notch generally illustrated at 80. First and second angle brackets 82, 84 each extend between the base 62 and the fourth base wall 70 so as to define a lock-bolt passage 86. The lock-bolt passage 86 extends through the third base notch 80.

A third base registration post assembly 88 extends from the base 62 and the third base wall 68. The third base wall 68 is further characterized by first and second gudgeons 90, 92. As will be described further below, the third base registration post assembly 88 and the first and second gudgeons 90, 92 engage a portion of the coverplate 58.

The Remote Station Housing Assembly: The Coverplate Referring to Figure 5, the coverplate 58 will now be further described. The coverplate 58 includes a cover slab 94 having a thickness corresponding to the height that the four base walls 64, 66, 68, 70 extend from the base 62 and having an area corresponding to the area defined between the four base walls

64, 66, 68, 70 such that the cover slab 94 is substantially receivable within the space defined between the base 62 and the four base walls 64, 66, 68, 70.

In this regard, the cover slab 94 defines first, second, third, fourth, and fifth registration cavities 96, 98, 100, 102, 104 that respectively cooperate with the first, second and third base registration post assemblies 76, 78, 88 and the first and second angle brackets 82, 84 to respectively accept the same therein.

The cover slab 94 also includes a circumscribing flange 106 that abuts the exterior edge of the four base walls 64, 66, 68, 70 when the cover slab 94 is inserted therebetween. The cover slab 94 further includes first and second pintles 108, 110 which cooperate with the first and second gudgeons 90, 92 to create a hinge mechanism wherein the coverplate 58 and the baseplate 60 are the leaves.

First and second spurs 1 12, 1 14 each extend from the cover slab 94 so as to respectively define with the cover slab 94 first and second lock-bolt slots 116, 1 18. The first and second spurs 112, 1 14 are so located on the cover slab 94 that when the cover slab 94 is fully inserted between the four base walls 64, 66, 68, 70, the lock-bolt slots 1 16, 1 18 are collinear with, and therefore form a portion of, the lock-bolt passage 86 defined by the first and second angle brackets 82, 84 on the baseplate 60.

Referring now to Figures 5 and 6, first, second, and third vampire terminals 120, 122, 124 extend from the cover slab 94. The vampire terminals are electrically conductive and sufficiently strong and sharp to pierce through the substrate 42 of the harness 38 to electrically contact the conductive strip 54. Each vampire terminal 120, 122, 124 is circumscribed by a gasket 126, which is sized and shaped to respectively engage one of the set of counterbores 56 in the harness 38 substrate 42.

With the cover slab 94 partially inserted into the base 60 and the harness 38 registered therebetween in its loop configuration, the first, second, and third vampire terminals 120, 122, 124 respectively align with one of the set of counterbores 56 in the harness 38. With the cover slab 94 fully inserted into the base 60 and the harness 38 registered therebetween in its loop configuration, the first, second, and third vampire terminals 120, 122, 124 contact the conductive strip 54 through the harness substrate 42 while the gaskets 126 seal the counterbores 56.

The Remote Station Housing Assembly: The Lock-Bolt

Referring now to Figure 7, a lock-bolt is illustrated generally at 128. The lock- bolt 128 includes a handle 130 and a bolt 132. The handle 130 defines a second keyhole 134 having an identical cross-section to the first keyhole 48 in the harness 38 and thus having a substantially circular cross-section augmented by a second pair of opposing notches 136. Within the second keyhole 134, a resilient pair of opposing pawls 138 taper from the perimeter toward the centre of the second keyhole 134 The pair of opposing pawls 138 are arranged in quadrature with the second pair of opposing notches 136

The bolt 132 is sized and shaped to cooperate with the lock-bolt passage 86 to be received and retained therein

The Remote Station Housing Assembly The Key

Referring now to Figure 8, a key is generally illustrated at 140 At one end, the key 140 is characterized by a broad head 142 The head 142 is shaped as a squat cylinder having a longitudinal axis collinear with the longitudinal axis of the key 140 as a whole One face of the cylindrical head 142 defines an angular socket 144 suitable for accepting a tool bit

The key 140 further includes a cylindrical shaft 146, which coaxially abuts the head 142 opposite the socket 144 The shaft 146 has a substantially smaller diameter than the head 142 In fact, the diameter of the shaft 146 is substantially the same as the diameter of the first and second keyholes 48, 134 to permit the shaft to fit snugly therewithin

The end of the shaft 146 opposite the head 142 is right tapered at an angle corresponding to the taper of the pair of opposing pawls 138 within the second keyhole 134, such that when the shaft 146 is within the second keyhole 134, the tapered end of the shaft 146 abuts and thereby buttresses the pair of opposing pawls 138 The tapered end of the shaft 146 terminates in a breakaway joint 148 Th e key 140 further includes a catch generally illustrated at 150. The catch 150 includes a disc 152 abutting the breakaway joint 148 and having a normal axis coaxial with the longitudinal axis of the key 140 as a whole. The diameter of the disc 152 is small enough to pass through the first and second keyholes 48, 134 but large enough to engage the pair of opposing pawls 138.

A pair of opposing tabs 154 extends from the perimeter of the disc 152. The pair of opposing tabs 154 is sized and shaped to correspond to and cooperatingly engage for sliding therewithin the second pair of opposing notches 136 in the lock-bolt 128.

The face of the disc 152 opposite the breakaway joint 148 is right tapered at an angle corresponding to the taper of the pair of opposing pawls 138 within the second keyhole 134 to form a tip 156. As will be described further below, the shape of the tip 156 enables the key 140 to temporarily displace the resilient pair of opposing pawls 138 when the key is inserted into the first and second keyholes 48, 134.

Although the key 140 has been described in terms of discrete portions, it should be understood that, desirably, the key is formed as an integrated whole.

The Remote Circuit Module

Referring now to Figure 9, the remote circuit module 34 is illustrated in further detail. The remote circuit module 34 includes a microprocessor circuit ("remote microprocessor circuit") generally illustrated at 158. The remote microprocessor circuit 158 is in communication with memory devices including random access memory ("remote RAM") 160 and read-only memory ("remote ROM") 162. Conventional address, data, and control signal lines are used by the remote microprocessor circuit 158 to read from each of the memory devices and to write to the remote RAM 160. ln this embodiment, the remote microprocessor circuit 158 includes a remote microprocessor 164 and various other conventional microprocessor circuit components including signal buffers and the like as will be appreciated by those skilled in the art, rendering the remote microprocessor 164 operable to communicate with the remote RAM 160 and the remote ROM 162. Generally the remote microprocessor circuit 158 establishes an address space with the remote RAM 160 and the remote ROM 162 mapped to respective areas of the address space.

The remote microprocessor circuit 158 includes a plurality of interface circuits, some of which may be located on the remote microprocessor 164 and some of which may be remote from the remote microprocessor 164. These interface circuits establish a plurality of I/O ports within a designated address space through which communications between the remote microprocessor circuit 158 and the various components described above are conducted. Such communications are conducted by writing to or reading from ports associated with a given interface or component described above.

In this embodiment, the interface circuits include a Transmit Data Buffer 166, a Carrier Frequency Register 168, a Transmitter Enable Register 170, a Housing

Open Event Register 172, a Harness Sever Event Register 174, and a Harness Tamper Event Register 176.

The Transmit Data Buffer 166 is a multi-byte shift register writable by the remote microprocessor circuit 158. The Transmit Data Buffer 166 has a serial output 178 connected to a modulating voltage controlled oscillator 180 at its control terminal 182. The Transmit Data Buffer 166 rolls its bits until reloaded instead of merely shifting the bits out of the register.

The modulating voltage controlled oscillator 180 also has an output terminal

184. In response to a digital active signal at its control terminal 182, the modulating voltage controlled oscillator 180 generates at its output terminal 184 a signal having a first frequency. In response to the absence of a digital active signal at its control terminal 182, the modulating voltage controlled oscillator 180 generates at its output terminal 184 a signal having a second frequency.

A mixer 186 has first and second input terminals 188, 190 and an output terminal 192. The first input terminal 188 of the mixer 186 is connected to the output terminal 184 of the modulating voltage controlled oscillator 182.

The Carrier Frequency Register 168 is a byte-wide register writable by the remote microprocessor circuit 158. The Carrier Frequency Register 168 has an output bus 194 connected to a digital to analogue converter 196 through a digital input bus 198. The digital to analogue converter 196 has an analogue output terminal 200 for generating an analogue voltage corresponding to a digital signal present at its input bus 198.

A carrier voltage controlled oscillator 202 has a control terminal 204 and an output terminal 206 for generating an output signal having a frequency corresponding to a voltage present at its control terminal 204. The carrier voltage controlled oscillator 202 is connected through its control terminal 204 to the output terminal 200 of the digital to analogue converter 196.

The mixer 186 is connected through its second input terminal 190 to the output terminal 206 of the carrier voltage controlled oscillator 202. The mixer generates at its output terminal 192 a signal corresponding to the superposition of the signals received at its first and second input terminals 188, 190.

The transmitter 36 has an input terminal 208 which is connected to the output terminal 192 of the mixer 186 to receive the signal mixed therein. The transmitter 36 also has an output terminal 210 connected to an antenna 212 for transmitting the signal received at the transmitter input terminal 208. Th e transmitter 36 also has a control terminal 214 In response to a digital active signal present at its control terminal 214, the transmitter 36 transmits the signal present at its input terminal 208 In response to the absence of a digital active signal at its control terminal 214, the transmitter 36 transmits no signal

The Transmitter Enable Register 170 is a one-bit register writable by the remote microprocessor circuit 158 The Transmitter Enable Register has an output terminal 216 for providing an digital output signal corresponding to the state of the Transmitter Enable Register 170 The Transmitter Enable Register output terminal 216 is connected to the control terminal 214 of the transmitter 36

The Housing Open Event Register 172 is a one-bit register enabled to interrupt the remote microprocessor circuit 158 In response to a digital active signal stored in the Housing Open Event Register 172, the remote microprocessor circuit 158 is interrupted

The Housing Open Event Register 172 includes an input terminal 220 through which it is connected to an output terminal 222 of a first comparator 224 The first comparator 224 has first and second input terminals 226, 228 The first input terminal 226 is connected to a first voltage reference source VREF1 The second input terminal 228 is connected to a first voltage divider network 230 at its centre tap, which in this embodiment is the second vampire terminal 122

When the voltage level at the second input terminal 228 of the first comparator 224 is greater than the voltage level at the first input terminal 226, then the output terminal 222 assumes a digital active level Alternatively, when the voltage level at the second input terminal 228 of the first comparator 224 is less than the voltage level at the first input terminal 226, then the output terminal 222 assumes a digital inactive level The first voltage divider network 230 also includes a source node, which in this embodiment is the first vampire terminal 120. The first vampire terminal is connected to a second reference voltage source VREF2.

The upper branch of the first voltage divider 230 is a first resistance 232 that connects the first vampire terminal 120 to the second vampire terminal 122. This first resistance 232 is actually that portion of the conductive strip 54 that extends between the first and second vampire terminals 120, 122.

The first voltage divider network 230 further includes a ground node 234. The lower branch of the first voltage divider 230 is a discrete first resistor 236 that connects the second vampire terminal 122 to the ground node 234. The first resistor 236 is selected with respect to the first voltage reference source VREF1 and the second voltage reference source VREF2 so that under normal operating conditions, the voltage level at the second input terminal 228 of the first comparator 224 is greater than the voltage level at the first input terminal 226, and thus the output terminal 222 assumes a digital active state.

The Harness Sever Event Register 174 is a one-bit register enabled to interrupt the remote microprocessor circuit 158. In response to a digital active signal stored in the Harness Sever Event Register 174, the remote microprocessor circuit 158 is interrupted.

The Harness Sever Event Register 174 includes an input terminal 236 through which it is connected to an output terminal 238 of a second comparator 240.

The second comparator 240 has first and second input terminals 242, 244. The first input terminal 242 is connected to a third voltage reference source VREF3. The second input terminal 244 is connected to a second voltage divider network 246 at its centre tap, which in this embodiment is the third vampire terminal 124. When the voltage level at the second input terminal 244 of the second comparator 240 is greater than the voltage level at the first input terminal 242, then the output terminal 238 assumes a digital active level. Alternatively, when the voltage level at the second input terminal 244 of the second comparator 240 is less than the voltage level at the first input terminal 242, then the output terminal 238 assumes a digital inactive level.

The second voltage divider network 246 also includes a source node, which in this embodiment is the first vampire terminal 120. The first vampire terminal is connected to the second reference voltage source VREF2.

The upper branch of the second voltage divider 246 is a second resistance 248 that connects the first vampire terminal 120 to the third vampire terminal 124. This second resistance 248 is actually that portion of the conductive strip 54 that extends between the first and third vampire terminals 120, 124.

The second voltage divider network 246 further includes the ground node 234. The lower branch of the second voltage divider 246 is a discrete second resistor 250 that connects the third vampire terminal 124 to the ground node 234. The second resistor 250 is selected with respect to the second voltage reference source VREF2 and the third voltage reference source VREF3 so that under normal operating conditions, the voltage level at the second input terminal 244 of the second comparator 240 is greater than the voltage level at the first input terminal 242, and thus the output terminal 238 assumes a digital active state.

The Harness Tamper Event Register 176 is a 1 -byte register readable by the remote microprocessor circuit 158. The Harness Tamper Event Register 176 includes an input terminal 252 through which it is connected to a digital output bus 254 of an analogue to digital converter 256. So connected, the Harness

Tamper Event Register 176 can latch the digital signal output by the analogue to digital converter 256. The analogue to digital converter 256 also has an input terminal 258 through which it is connected to the centre tap of the second voltage divider network 246, that centre tap being the third vampire terminal 124 Thus, the Harness Tamper Event Register 176 latches a digital representation of the centre tap voltage level of the second voltage divider 246

The remote ROM 162 is configured to include a set of constants 260 The constant XI D 262 uniquely identifies transmissions from a particular remote station 14

The constant F1 264 represents a first transmitter carrier frequency The constant F2 266 represents a second transmitter carrier frequency

The constant dR 268 represents the maximum allowable change in voltage level at the third vampire terminal 124, which corresponds to a maximum allowable change in resistance in the portion of the conductive strip 54 extending between the first and third vampire terminals 120, 124

The constants ACTIVE 270 and INACTIVE 272 represent respectively active and inactive digital signal states Finally, the constants NORMAL 274 and VIOLATION 276 represent respectively normal and violation states for status indicators

The remote ROM 162 is further programmed with sets of codes readable by the remote microprocessor 164 The sets of codes define respective routines for directing the microprocessor to interact with the I/O ports to establish certain functionality according to conventional algorithms and according to new algorithms described herein New algorithms according to this embodiment of the invention are implemented by routines including a REMOTE MAIN LOOP

278 and an INTERRUPT routine 280 The remote RAM 160 is configured to include a plurality of buffers, including a Harness Sever Status Buffer 282, a Harness Tamper Status Buffer 284, a Housing Open Status Buffer 286, a Harness Resistance Buffer 288, and a Transmit Now Buffer 290.

The Harness Sever Status Buffer 282 is loaded with codes representing whether the harness 38 is in a normal operating state or a severed violation state. Thus, the Harness Sever Status Buffer 282 can be loaded with either the constant NORMAL 274 or the constant VIOLATION 276.

The Harness Tamper Status Buffer 284 is loaded with codes representing whether the harness 38 is in a normal operating state or a tampered violation state. Thus, the Harness Tamper Status Buffer 284 can be loaded with either the constant NORMAL 274 or the constant VIOLATION 276.

The Housing Open Status Buffer 286 is loaded with codes representing whether the remote station housing assembly 32 is in a normal operating state or an opened violation state. Thus, the Housing Open Status Buffer 286 can be loaded with either the constant NORMAL 274 or the constant VIOLATION 276.

The Harness Resistance Buffer 288 is loaded with codes representing the penultimate voltage level measurement at the third vampire terminal 124, and correspondingly the penultimate resistance measurement of that portion of the conductive strip 54 that extends between the first and third vampire terminals

120, 124.

The Transmit Now Buffer 290 is loaded with codes representing whether the remote station 14 should immediately transmit a status report to the base station 12 or whether it should wait until the next scheduled transmission. Thus the Transmit Now Buffer 290 can be loaded with either the constant ACTIVE 270 or the constant INACTIVE 272. The Base Circuit Module

Referring now to Figure 10, the base circuit module 16 is described in further detail. It is understood that the base circuit module 16 has conventional provisions for both main and backup electrical power, neither of which is illustrated in detail.

The base circuit module 16 includes a microprocessor circuit ("base microprocessor circuit") generally illustrated at 300. The base microprocessor circuit 300 is in communication with memory devices including random access memory ("base RAM") 302, and read-only memory ("base ROM") 304. Conventional address, data, and control signal lines are used by the base microprocessor circuit 300 to read from each of the memory devices and to write to the base RAM 302.

In this embodiment, the base microprocessor circuit 300 includes a base microprocessor 306 and various other conventional microprocessor circuit components including signal buffers and the like as will be appreciated by those skilled in the art, rendering the base microprocessor 306 operable to communicate with the base RAM 302 and the base ROM 304. Generally the base microprocessor circuit 300 establishes an address space with the base RAM 302 and the base ROM 304 mapped to respective areas of the address space.

The base circuit module 16 also includes the receiver 22, which has an input terminal 326 connected to an antenna 328 to receive a radio frequency signal electromagnetically coupled to the antenna 328. The receiver 22 has an output terminal 330 to which it provides the received radio frequency signal.

A demodulator 332 is connected through an input terminal 334 to the output terminal 330 of the receiver 22 to receive the radio frequency signal. The demodulator 332 also has an output terminal 336 to which it provides a demodulated received signal.

A detector 338 having an input terminal 340 and an output terminal 342 is connected through its input terminal 340 to the output terminal 336 of the demodulator 332 to receive the demodulated signal. The detector 338, in this embodiment a simple comparator, presents at its output terminal 342 a digital serial representation of the analog demodulated signal received at its input terminal 340.

The demodulator 332 also has an mixing terminal 344 for receiving a mixing signal. A voltage controlled oscillator 346 having a control terminal 348 and an output terminal 350 is connected through its output terminal 350 to the mixing terminal 344 of the demodulator 332 to provide the mixing signal. In response to a voltage signal presented at its control terminal 348, the voltage-controlled oscillator 346 presents an oscillating signal of a corresponding frequency at its output terminal 350.

A digital to analogue converter 352 has an input bus 354 and an output terminal 356. The digital to analogue converter 352 is connected through its output terminal 356 to the control terminal 348 of the voltage controlled oscillator 346 to provide a control voltage signal. The control voltage signal at the output terminal 356 of the digital to analogue converter 352 corresponds to the digital signal at its input bus 354.

Along another circuit path, a rectifier 358 has an input terminal 360 and an output terminal 362. The rectifier input terminal 360 is connected to the output terminal 336 of the demodulator 332 to receive the demodulated signal. The rectifier 358 presents a rectified signal at its output terminal 362.

A lowpass filter 364 having an input terminal 366 and an output terminal 368 is connected through its input terminal 366 to the rectifier output terminal 362 to average the rectified signal. The lowpass filter 364 presents this averaged signal at its output terminal 368.

An analogue to digital converter 370 has an input terminal 372 and an output bus 374. The analogue to digital converter 370 is connected through its input terminal 372 to the output terminal of the lowpass filter. At its output bus 374, the analogue to digital converter 370 presents a digital representation of the averaged signal.

The base microprocessor circuit 300 includes a plurality of interface circuits, some of which may be located on the base microprocessor 306 and some of which may be remote from the base microprocessor 306. These interface circuits establish a plurality of I/O ports within a designated address space through which communications between the base microprocessor circuit 300 and the various components described above are conducted. Such communications are conducted by writing to or reading from ports associated with a given interface or component described above.

In this embodiment, the interface circuits include a Receive Buffer 308, a Received Signal Strength (RSS) Register 310, a Demodulating Frequency

Register 312, a Motion Register 314, a Power Register 316, a Telephone Register 318, a Modem Interface 320, a Keypad Interface 322, and a Display Interface 324.

The Receive Buffer 308 is a multi-byte shift register readable by the base microprocessor 306. The Receive Buffer 308 has an input terminal 376 connected to the output terminal 342 of the detector 338 to receive the digital representation of the demodulated signal.

The Received Signal Strength (RSS) Register 310 is a byte-wide register readable by the base microprocessor 306. The RSS Register 310 has an input terminal 378 connected to the output bus 374 of the analogue to digital converter 370 to receive the digital representation of the average rectified received signal.

The Demodulating Frequency Register 312 is a byte-wide register writable by the base microprocessor 306. The Demodulating Frequency Register 312 has an output bus 380 connected to the input bus 354 of the digital to analogue converter 352 to present a digital signal for conversion to the analog control voltage signal.

The Motion Register 314 is a bit-wide register readable by the base microprocessor 306. The Motion Register has an input terminal 382 connected to an output terminal 384 of a conventional motion detector 386. Upon detecting motion of the base station 12, the motion detector 386 generates a digital active signal at its output terminal 384, thereby setting the Motion Register 314 active.

The Power Register 316 is a bit-wide register readable by the base microprocessor 306. The Power Register has an input terminal 388 connected to an output terminal 390 of a conventional electricity sensor 392. Upon detecting a loss of electricity to the base station 12, the electricity sensor 386 generates a digital active signal at its output terminal 390, thereby setting the Power Register 316 active.

The Telephone Register 318 is a bit-wide register readable by the base microprocessor 306. The Telephone Register 318 has an input terminal 394 connected to an output terminal 396 of a conventional telephone loop sensor 398. Upon detecting a broken telephone loop at the base station 12, the telephone loop sensor 398 generates a digital active signal at its output terminal 396, thereby setting the Telephone Register 318 active.

The Modem Interface 320 is conventional and is readable and writable by the microprocessor 306. The Modem Interface 320 is associated with a conventional modem 400 which is in turn connectable to a communications circuit, in this embodiment a public switched telephone network 30. The Modem Interface 320 enables the base microprocessor 306 to exchanging data with other devices over the public switched telephone network 30, in this embodiment a central monitoring computer administered by the State (not shown).

The Keypad Interface 322 has a keypad interface input 404 and a keypad interface output 406. The keypad interface input 404 is connected to the keypad 18. The keypad interface output 408 is connected to the base microprocessor 306. In response to distinct keypress actions at the keypad 18, the keypad interface 322 generates distinct signals readable by the microprocessor 306 at the keypad interface output 408.

The Display Interface 324 has a display interface input 410 and a display interface output 412. The display interface input 410 is connected to the base microprocessor 306 and the display interface output 412 is connected to a visual display 20, which in this embodiment is a liquid crystal display. In response to signals received from the base microprocessor 306, the Display Interface 324 issues signals to the visual display 20 to cause a corresponding image to appear on the visual display 20.

The base ROM 304 is configured to include a set of constants 900. The constant MAXTIME 902 represents a counter value afterwhich a counter should be reset to zero. The constant TIMER START 904 represents an initial value for a downcounter.

The constant F1 906 represents a first demodulating frequency. The constant F2 908 represents a second demodulating frequency.

The constants ACTIVE 910 and INACTIVE 912 respectively represent active and inactive digital signal states. The constant LIM 914 represents a maximum time duration for the receiver 22 to be tuned to one frequency.

The constant ESCAPE TIME 916 represents a time duration since a signal was last received from the remote station 14 afterwhich it may be inferred that the monitoree has escaped from the monitored area.

The constant OUT OF BOUNDS 918 represents a value used to flag a situation in which a signal has been received at the receiver 22 from the remote station

14 but the signal is so weak that one may infer that the monitoree has strayed from the monitored area.

The constants A 920, B 922, and A&B 924 represent keypress combinations as signified by the keypad interface 404.

The constants MAXIMUM 926, MEDIUM 928, and MINIMUM 930 represent received signal strength thresholds.

The base ROM 304 is further programmed with sets of codes readable by the base microprocessor 306. The sets of codes define respective routines for directing the microprocessor 306 to interact with the I/O ports to establish certain functionality according to conventional algorithms and according to new algorithms described herein. New algorithms according to this embodiment of the invention are implemented by routines including a BASE MAIN LOOP routine 932, a TIMER CONTROL routine 934, a RECEIVER CONTROL routine 936, a SETUP RANGES routine 938, a LOCATE TRANSMITTER routine 940, a DETECT TAMPERING routine 942, a REPORT STATUS routine 944, a CALIBRATE RANGE routine 946, a PREDEFINED RANGE routine 948, a PROGRESSIVE RANGES routine 950, and an INTERRUPT routine 280. The base RAM 302 is configured to include a plurality of buffers, including a Motion Timer 952, a Utility Timer 954, a Timer 956, a Last Xmit Timer 958, a Clk Buffer 960, a Received Signal Strength Indicator (RSSI) Buffer 962, an Index Buffer 964, a Loop Buffer 966, an Escaped Buffer 968, a Location Buffer 970, a Motion Info Buffer 972, a Motion Alarm Buffer 974, a Utility Alarm Buffer

976, a Minimum RSS buffer 977, a Range Count Buffer 978, a Range Buffer 980, and a Log Buffer 982.

The Motion Timer 952 is loaded with codes representing the unexpired portion of a time interval initiated by movement of the base station 12 during which disconnecting either the power input 24 or the communication connection 28 will trigger a motion alarm. The Motion Timer 952 counts by the second.

The Utility Timer 954 is loaded with codes representing the unexpired portion of a time interval initiated by disconnection of either the power input 24 or the communication connection 28 during which moving the base station 12 will trigger a motion alarm. The Utility Timer 954 counts by the second.

The Timer 956 is loaded with codes representing an incrementing time interval resolved to the second.

The Last Xmit Timer 958 is loaded with codes representing the number of minutes since the last signal was received from the remote station 14.

The Clk Buffer 960 is loaded with codes representing an incrementing date and time resolved to the second.

The RSSI Buffer 962 is a bit-wide buffer that is loaded with the constant ACTIVE 910 when a signal from the remote station 14 has been detected at the Received Signal Strength (RSS) Register 310. The Index Buffer 964 and the Loop Buffer 966 are loaded with codes representing integer counter values.

The Escaped Buffer 968 is a bit-wide buffer that is loaded with the constant ACTIVE 910 when a signal from the remote station 14 has not been received for a predetermined period of time.

The Location Buffer 970 is loaded with codes representing the location of the monitoree with respect to the monitored area. As will be described further below, the monitored area can be divided by a series of substantially concentric range contours and thus the Location Buffer 970 is loaded with codes representing which of the contours the monitoree is located within. If the monitoree is located outside of the monitored area, then the Location Buffer 970 is loaded with the constant OUT OF BOUNDS 918. Thus, the constant OUT OF BOUNDS 918 must be easily distinguishable from the other codes.

The Motion Info Buffer 972, the Motion Alarm Buffer 974, and the Utility Alarm Buffer 976 are each bit-wide buffers respectively loaded with the constant ACTIVE 910 when respective predetermined trigger conditions have occurred.

The Minimum RSS Buffer 977 is a byte-wide buffer loaded with codes representing a received signal strength.

The Range Count Buffer 978 is loaded with codes representing the number of contour regions that the monitored area has been divided into.

The Range Buffer 980 is configured as a one dimensional array, loaded with codes respectively representing the expected received signal strength of respective signals transmitted by the remote station 14 when located at respective monitored area contours. The Log Buffer 982 is configured as a two dimensional array. The first dimension represents log entry records while the second dimension represents record fields.

Each record in the Log Buffer 982 has two fields. The first field is loaded with codes representing the value of the Clk Buffer 960 at the time that the record was written.

The second field in each Log Buffer 982 record is loaded with codes representing a status word, where each bit or group of bits in the status word represents a specific condition. Three bits in the status word are respectively mapped to the Harness Sever Status Buffer (282), the Harness Tamper Status Buffer (284) and the Housing Open Status Buffer (286) all received at the receiver 22 from the remote station 14 and decoded into the Receive Buffer 308. Four bits in the status word are respectively mapped to the Escaped

Buffer 968, the Motion Info Buffer 972, the Motion Alarm Buffer 974, and the Utility Alarm Buffer 976. The status word further allocates five bits to represent the contents of the Location Buffer 970.

Operation

Assembling the Remote Station and Securing to the Monitoree

Referring now to Figures 1 through 8, assembling and securing the remote station 14 will now be discussed.

The broad exterior surface of the baseplate 60 is abutted against one of the monitoree's limbs (not shown). The harness 38 is then wrapped into its looped configuration so that the limb passes through the aperture 40 so defined.

The first set of registration holes 44 on the harness 38 is then secured over the first registration post assembly 76 on the baseplate 60. One member of the second set of registration holes 46 on the harness 38 is then selected for engagement with the second registration post assembly 78 on the baseplate 60. This selection is made such that the harness 38 grips the limb securely yet comfortably.

For safety, the strain-relief notch 50, which is the structurally weakest point of the harness substrate 42, enables the harness 38 to break before the monitoree is injured should the harness 38 become caught during use. A harness 38 having appropriate strength can be selected according to the nature of the monitoree and the particular circumstances of the detention.

If a free portion of the harness extends beyond the second registration post assembly 78, then it may be severed, taking care not to weaken the member of the second set of registration holes 46 engaged with the second registration post assembly 78. It is to be noted, however, that the tampering detection capability of the remote station 14 is not impaired if the harness surface shell 55 is breached at one end and the conductive strip 54 thereby becomes exposed to the environment.

In this way, the harness passes transversely through the first and second notches 72, 74 in the baseplate 60 and engages the interior of the baseplate 60. Similarly, the baseplate is secured to the monitoree's limb by the harness.

The next step is to engage the coverplate 58 to the baseplate 60. In this regard, the first and second pintles 108, 1 10 are inserted into the first and second gudgeons 90, 92 to form the coverplate 58 and the baseplate 60 into a hinge. The coverplate 58 is then rotated about the hinge axis toward the baseplate so that the cover slab 94 is inserted within the volume defined between the base 62 and the four base walls 64, 66, 68, 70.

During this rotation, the first, second, third, fourth, and fifth registration cavities 96, 98, 100, 102, 104 within the cover slab 94 respectively cooperate with the first, second and third base registration post assemblies 76, 78, 88 and the first and second angle brackets 82, 84 to respectively accept the same therein.

Within the interior of the remote station housing assembly 32, the first, second, and third vampire terminals 120, 122, 124 align with corresponding select counterbores 57 in the harness surface shell 55 as best seen in Figure 6A.

As best seen in Figure 6B, as the coverplate 60 rotation completes, the three vampire terminals 120, 122, 124 each pierce the harness surface shell 55 and the conductive strip 54 to extend into select wells 56 within the tough substrate

42 By extending into the select wells 56, the three vampire terminals 120, 122, 124 enjoy improved surface contact and thus electrical contact with respective portion of the conductive strip 54

The piercing action of the three vampire terminals 120, 122, 124 wipes them clean and helps to seal them from impurities which might otherwise undesirably affect their electrical properties. For even more protection against impurities, the three vampire terminals 120, 122, 124 are each sealed within respective counterbores 57 by respective gaskets 126

When the rotation is complete, the flange 106 circumscribing the cover slab 94 abuts the exterior edge of the four base walls 64, 66, 68, 70

To restrain the coverplate 58 and the baseplate 60 from rotating or being rotated open again, the lock-bolt 128 is inserted within the lock-bolt passage 86 to engage the first and second angle brackets 82, 84 on the baseplate 60 and the first and second spurs 1 12, 1 14 on the coverplate 58

To prevent the lock-bolt 128 from being withdrawn, the first keyhole 48 in the harness 38 is aligned with the second keyhole 134 in the lock-bolt 128 and the key 140 is aligned with both the first and second keyholes 48, 134. The key

140 is then pressed tip 156 first into the first and second keyholes 48, 134 such that the tapered tip 156 temporarily displaces the resilient pair of opposing pawls 138 within the second keyhole 134.

When the key 140 has been pressed sufficiently far into the second keyhole 134, the pair of opposing pawls 138 clear the catch 150 and spring back against the tapered shaft 146. In this position, the pair of opposing pawls 138 oppose any outward movement of the key 140 by urging against the catch 150 and in particular the disc 152.

It should also be noticed that the key 140 is not free to rotate about its longitudinal axis because the pair of opposing tabs 154 on the catch 150 urge against the pair of opposing notches 136 in the second keyhole 134.

In this condition, the remote station housing assembly 32 is tightly locked and sealed against the environment and is secure by the harness 38 to the monitoree's limb. The first and second keyholes 48, 138 cannot move past the broad head 142 of the key 140. The lock-bolt 128 is retained in place by the harness 38 which is in turn retained in place by the first and second registration post assemblies 76, 78 within the remote station housing assembly 32.

Similarly, the harness 38, and in particular the harness aperture 40, cannot be adjusted without opening the remote station housing assembly 32.

To open the remote station housing assembly 32, a cooperating tool bit (not shown) is inserted into the socket 144 in the head 142 of the key 140. A torque is applied to the tool bit to urge the key 140 to rotate within first and second keyholes 48, 134. However, as discussed above, the key 140 is not free to rotate about its longitudinal axis because the pair of opposing tabs 154 on the catch 150 urge against the pair of opposing notches 136 in the second keyhole 134. If sufficient torque is applied to the key 140, the breakaway joint 148 will break and the catch 150 will be separated from the head 142. It will then be possible to withdraw the head 142 and the shaft 146 of the key 140 from the first and second keyholes 48, 134 and thus the lock-bolt 128 and the harness 38 will once again be free to move independently.

Operation of the Remote Circuit Module - Main Loop

Referring to Figures 2, 9, and 1 1 , the operation of the remote circuit module 34 REMOTE MAIN LOOP 278 will now be described. The first purpose of the REMOTE MAIN LOOP 278 is to schedule and implement status transmissions from the remote station 14 to the base station 12. The second purpose of the REMOTE MAIN LOOP 278 is to analyze changes in the resistance of the conductive strip 54 to determine whether the monitoree is tampering with the harness 38 or the remote station housing assembly 32.

Block 416 directs the remote microprocessor 164 to initialize the RAM buffers and the Transmitter Enable Register 170. More specifically, block 416 directs the microprocessor 164 to load the constant INACTIVE 272 into the Transmitter Enable Register 170 and the Transmit Now Buffer, to load the constant NORMAL 274 into the Harness Sever Status Buffer 282, the Harness Temper

Status Buffer 284, and the Housing Open Status Buffer 286, and to load the contents of the Harness Tamper Event Register 176 into the Harness Resistance Buffer 288.

Block 418 then directs the remote microprocessor 164 to latch a new value into the Harness Tamper Event Register 176 and to read that value.

Block 420 then directs the remote microprocessor 164 to determine whether the absolute value of the difference between the contents of the Harness Resistance Buffer 288 and the contents of the Harness Tamper Event Register

176 is less than the constant dR 268, which represents the maximum allowable difference. If the difference exceeds the constant dR 268, then a significant change in resistance has occurred in that portion of the conductive strip 54 that extends between the first and third vampire terminals 120, 124. That portion of the conductive strip 54 circumscribes the monitoree's limb. A significant change in resistance indicates that the monitoree has likely undertaken one of three actions.

First, the monitoree may have begun to cut through the conductive strip 54 and therefore the surrounding harness 38, thereby increasing the resistance of the conductive strip.

Second, the monitoree may have begun to stretch the conductive strip 54 and therefore the surrounding harness 38, thereby increasing the resistance of the conductive trip.

Third, the monitoree may have attached an electrical jumper between two points on the conductive strip in preparation for severing the conductive strip 54 and the surrounding harness 38.

All three actions constitute tampering with the harness 38 and therefore if such a change in resistance is detected at block 420, then block 422 directs the remote microprocessor 164 to store in the Harness Tamper Status Buffer the constant VIOLATION 276 before directing the remote microprocessor 164 forward to block 424.

Alternatively, if no such change in resistance has been detected at block 420, then block 424 directs the remote microprocessor 164 to load the Transmit Data Buffer with the constant XID 262 and the contents of the Harness Sever Status Buffer 282, the Harness Tamper Status Buffer 284, and the Housing

Open Status Buffer 286. Block 426 then directs the remote microprocessor 164 to load the Carrier Frequency Register with the constant F1 264 to select a first predetermined transmitting carrier frequency.

Block 428 then directs the remote microprocessor 164 to load the Transmitter

Register 166 with the constant ACTIVE 270 to enable the transmitter 36.

Block 430 then directs the remote microprocessor 164 to wait for one half second to permit sufficient transmission time for the data in the Transmit Data Buffer 166 to be transmitted at least once.

Block 432 then directs the remote microprocessor 164 to load the Transmitter Register 166 with the constant INACTIVE 272 to disable the transmitter 36.

Block 434 then directs the remote microprocessor 164 to load the Carrier

Frequency Register with the constant F2 266 to select a second predetermined transmitting carrier frequency.

Block 436 then directs the remote microprocessor 164 to load the Transmitter Register 166 with the constant ACTIVE 270 to enable the transmitter 36.

Block 438 then directs the remote microprocessor 164 to wait for one half second to permit sufficient transmission time for the data in the Transmit Data Buffer 166 to be transmitted at least once.

Block 440 then directs the remote microprocessor 164 to load the Transmitter Register 166 with the constant INACTIVE 272 to disable the transmitter 36.

Block 442 then directs the remote microprocessor 164 to wait for 15 seconds before directing the remote microprocessor 164 back to block 418 to re-execute the loop. This cycle may be exploited to place the microprocessor 164 into a battery-saving periodic sleep state, from which it awakes at regular intervals, in this embodiment every 15 seconds, or when interrupted, as will be described immediately below.

Operation of the Remote Circuit Module - Interrupt Routine Referring to Figures 2, 9, and 12, the operation of the remote circuit module 34

INTERRUPT ROUTINE 280 will now be described. The purpose of the INTERRUPT ROUTINE 280 is to cause the remote circuit module 24 to immediately issue a status report to the base station 12 in the event of a serious violation, in this embodiment severing the harness 38 or opening the remote station housing assembly 32.

Block 500 represents a logic test to determine both whether the Harness Sever Status Buffer 282 contains the constant NORMAL 274 and whether the Harness Sever Event Register 174 contains the constant ACTIVE 270.

If so, then a new Harness Sever Event has been detected. The Harness Sever Event Register 174 contains the constant ACTIVE 270 when the voltage level at the third vampire terminal 124 decreases significantly as a result of an interruption of the current flowing from the first vampire terminal 120 to the third vampire terminal 124 through the conductive strip 54 in the harness 38

Block 502 therefore interrupts the remote microprocessor 164 to load the constant VIOLATION 276 into the Harness Sever Status Buffer 282 and block 504 directs the remote microprocessor 164 to load the constant ACTIVE 270 into the Transmit Now Buffer 290 before directing the remote microprocessor

164 forward to block 512

Alternatively, if at block 500 either the Harness Sever Status Buffer 282 does not contain the constant NORMAL 274 or the Harness Sever Event Register 174 does not contain the constant ACTIVE 270, then either a known violation has been unnecessarily redetected or no violation has occurred respectively. The remote microprocessor 164 is therefore not interrupted Block 506 represents a logic test to determine both whether the Housing Open Status Buffer 286 contains the constant NORMAL 274 and whether the Housing Open Event Register 172 contains the constant ACTIVE 270.

If so, then a new Housing Open Event has been detected. The Housing Open Event Register 172 contains the constant ACTIVE 270 when the voltage level at the second vampire terminal 122 decreases significantly as a result of an interruption of the current flowing from the first vampire terminal 120 to the second vampire terminal 122 through the conductive strip 54 in the harness 38.

This situation arises when the remote station housing assembly 32 has been opened and at least one of the first and second vampire terminals 120, 122 have disengaged from the conductive strip 54.

Block 508 therefore interrupts the remote microprocessor 164 to load the constant VIOLATION 276 into the Housing Open Status Buffer 286 and block 510 directs the remote microprocessor 164 to load the constant ACTIVE 270 into the Transmit Now Buffer 290 before directing the remote microprocessor 164 forward to block 512.

Alternatively, if at block 506 either the Housing Open Status Buffer 286 does not contain the constant NORMAL 274 or the Housing Open Event Register 172 does not contain the constant ACTIVE 270, then either a known violation has been unnecessarily redetected or no violation has occurred respectively. The remote microprocessor 164 is therefore not interrupted.

Block 512 then directs the remote microprocessor 164 to determine whether the Transmit Now Buffer 290 contains the constant ACTIVE 270. If not, then the INTERRUPT ROUTINE 280 terminates.

Alternatively, if the Transmit Now Buffer 290 contains the constant ACTIVE 270, then block 514 directs the remote microprocessor 164 to load the Transmit Data Buffer with the constant XI D 262 and the contents of the Harness Sever Status Buffer 282, the Harness Tamper Status Buffer 284, and the Housing Open Status Buffer 286.

Block 516 then directs the remote microprocessor 164 to load the Carrier

Frequency Register with the constant F1 264 to select a first predetermined transmitting carrier frequency.

Block 518 then directs the remote microprocessor 164 to load the Transmitter Register 166 with the constant ACTIVE 270 to enable the transmitter 36.

Block 520 then directs the remote microprocessor 164 to wait for one half second to permit sufficient transmission time for the data in the Transmit Data Buffer 166 to be transmitted at least once.

Block 522 then directs the remote microprocessor 164 to load the Transmitter Register 166 with the constant INACTIVE 272 to disable the transmitter 36.

Block 524 then directs the remote microprocessor 164 to load the Carrier Frequency Register with the constant F2 266 to select a second predetermined transmitting carrier frequency.

Block 526 then directs the remote microprocessor 164 to load the Transmitter Register 166 with the constant ACTIVE 270 to enable the transmitter 36.

Block 528 then directs the remote microprocessor 164 to wait for one half second to permit sufficient transmission time for the data in the Transmit Data Buffer 166 to be transmitted at least once.

Block 530 then directs the remote microprocessor 164 to load the Transmitter

Register 166 with the constant INACTIVE 272 to disable the transmitter 36. Block 532 then directs the remote microprocessor 164 to load the Transmit Now Register 290 with the constant INACTIVE 272 to clear the transmission urgency, before the INTERRUPT ROUTINE 280 terminates.

Operation of the Base Circuit Module - BASE MAIN LOOP

With reference to Figures 10 and 13, the operation of the BASE MAIN LOOP 932 will now be further described.

Block 550 directs the base microprocessor 306 to initialize the buffers in the base RAM 302 when the base circuit module 16 is first powered up or reset.

To this end, the Motion Timer 952, the Utility Timer 954, the Timer 956, and the Last Xmit Timer 958 are zeroed. The Clk Buffer 960 is loaded with codes representing the current time and date.

The RSSI Buffer 962, the Escaped Buffer 968, the Motion Info Buffer 972, the

Motion Alarm Buffer 974, and the Utility Alarm Buffer 976 are each loaded with the constant INACTIVE 912.

The Index Buffer 964 and the Location Buffer 970 are each loaded with codes representing the integer 1. The Range Count Buffer 978 is loaded with codes representing the integer 2. The first element of the Range Buffer 980 is loaded with the constant MINIMUM 930.

After initialization has occurred, three independent processes 552, 554, 556 are spawned in the base microprocessor 306. Each of the three processes 552,

554, 556 will be discussed in turn and each may be understood to be an independent routine directing the base microprocessor 306.

The first process 552 begins with block 558 which directs the base microprocessor 306 to execute the TIMER CONTROL subroutine 934. Upon completion of the TIMER CONTROL subroutine 934, block 560 directs the base microprocessor 306 to wait for an interrupt signal generated by a clock circuit (not shown) associated with the base microprocessor 306, the interrupt signal demarcating one second time intervals.

Upon the occurrence of the one-second interrupt signal, block 560 directs the base microprocessor 306 back to block 558.

The second process 554 begins with block 562 which directs the base microprocessor 306 to execute the RECEIVER CONTROL subroutine 936.

Upon completion of the RECEIVER CONTROL subroutine 936, the base microprocessor 306 is directed back to 562.

The third process 556 begins with block 564 which directs the base microprocessor 306 to execute the SETUP RANGES subroutine 938.

Upon completion of the SETUP RANGES subroutine 938, block 566 directs the base microprocessor 306 to execute the LOCATE TRANSMITTER subroutine 940.

Upon completion of the LOCATE TRANSMITTER subroutine 940, block 568 directs the base microprocessor 306 to execute the DETECT TAMPERING subroutine 942.

Upon completion of the DETECT TAMPERING subroutine 942, block 570 directs the base microprocessor 306 to execute the REPORT STATUS subroutine 944.

The REPORT STATUS subroutine is conventional and will be discussed only briefly herein. Both at predetermined intervals and in response to conditions indicative of inappropriate monitoree behaviour as recorded in the Log Buffer

982 and the buffers mapped therein, the base microprocessor 306 will direct the Modem Interface 320 to cause the modem 400 to connect to the public switched telephone network 30 and to engage the central monitoring computer administered by the State (not shown) to upload the Log Buffer 982.

After the Log Buffer 982 has been uploaded to the central monitoring computer, the Index Buffer 964 is reloaded with a code representing the integer 1 in order to flush the Log Buffer 982. Once the Report Status subroutine 944 has completed, the base microprocessor 306 is directed back to block 564.

Operation of the Base Circuit Module - TIMER CONTROL

Referring to Figures 10 and 14, the TIMER CONTROL subroutine 934 will now be discussed in further detail. The TIMER CONTROL subroutine 934 updates each of the timer buffers in the base RAM 302 after the base microprocessor 302 has received an interrupt signal demarcating a new one second time interval.

Block 580 directs the base microprocessor 306 to determine whether the value stored in the Motion Timer 952 is greater than zero. If not, then the base microprocessor 306 is directed forward to block 582. Alternatively if so, then block 584 directs the base microprocessor 306 to decrement the Motion Timer

952, afterwhich the base microprocessor 306 is directed forward to block 582.

Block 582 directs the base microprocessor 306 to determine whether the value stored in the Utility Timer 954 is greater than zero. If not, then the base microprocessor 306 is directed forward to block 586. Alternatively if so, then block 588 directs the base microprocessor 306 to decrement the Utility Timer 954, afterwhich the base microprocessor 306 is directed forward to block 586.

Block 586 directs the base microprocessor 306 to determine whether the value stored in the Timer 956 divides evenly by the integer 60, which result would indicate that a minute has just passed. If not, then the base microprocessor

306 is directed forward to block 590. Alternatively if so, then block 592 directs the base microprocessor 306 to increment the Last Xmit Timer 958 to indicate that another minute has passed since the last transmission from the remote station 14 was received. Thereafter, the base microprocessor 306 is directed forward to block 590.

Block 590 directs the base microprocessor to determine whether the value stored in the Timer 956 is equal to the constant MAXTIME 902. If not, then the base microprocessor 306 is directed forward to block 594. Alternatively if so, then block 596 directs the base microprocessor 306 to load the Timer 956 with codes representing the integer zero in order to predictably reset the Timer 956 to prevent it from wrapping around. Thereafter, the base microprocessor 306 is directed forward to block 594.

Block 594 directs the base microprocessor 306 to increment the Clk Buffer 960, afterwhich the TIMER CONTROL subroutine 934 terminates and the base microprocessor 306 is directed back to the calling routine.

Operation of the Base Circuit Module - RECEIVER CONTROL Referring now to Figures 10 and 15, the operation of the RECEIVER CONTROL subroutine 936 will now be described. In general terms, the

RECEIVER CONTROL subroutine 936 scans for transmissions from the remote station 14 on various carrier frequencies, in this embodiment two carrier frequencies.

Block 600 directs the base microprocessor 306 to store in the Demodulating

Frequency Register 312 the constant F1 906 to cause the demodulator 332 to remove from the received signal a carrier signal having a first predetermined frequency.

Block 602 directs the base microprocessor 306 to store in the Timer 956 the value zero to reset the Timer 956. Block 604 directs the base microprocessor 306 to read the contents of the Received Signal Strength (RSS) Register 310 and block 606 directs the base microprocessor 306 to determine whether the contents of the RSS Register 310 is greater than zero.

If the contents of the RSS Register 310 is greater than zero, then block 608 directs the base microprocessor 306 to load the Received Signal Strength Indicator (RSSI) Buffer 962 with the constant ACTIVE 910 to indicate that a received signal has been detected.

Block 610 then directs the base microprocessor 306 to create a new record in the Log Buffer 982, the new record being assigned an array index value equal to the contents of the Index Buffer 964 and having field contents equal to the current contents of the Clk Buffer 960 and the current contents of the buffers mapped into the status word as described hereinabove in the definition of the

Log Buffer 982. Thereafter, block 612 directs the base microprocessor 306 to increment the contents of the Index Buffer 964 before directing the base microprocessor 306 forward to block 614.

Alternatively, if at block 606 the contents of the RSS Register 310 is not greater than zero, then block 616 directs the base microprocessor 306 to determine whether the contents of the Timer 956 is greater than the constant LIM 914. If not, then the base microprocessor 306 is directed back to block 604 to once again read the contents of the RSS Register 310. Alternatively, if the contents of the Timer 956 is greater than the constant LIM 914, then the base microprocessor 306 is directed forward block 614 under the assumption that it is not productive to keep looking for a signal at the current carrier frequency.

Block 614 directs the base microprocessor 306 to store in the Demodulating Frequency Register 312 the constant F2 908 to cause the demodulator 332 to remove from the received signal a carrier signal having a second predetermined frequency. Block 616 directs the base microprocessor 306 to store in the Timer 956 the value zero to reset the Timer 956.

Block 618 directs the base microprocessor 306 to read the contents of the

Received Signal Strength (RSS) Register 310 and block 620 directs the base microprocessor 306 to determine whether the contents of the RSS Register 310 is greater than zero.

If the contents of the RSS Register 310 is greater than zero, then block 622 directs the base microprocessor 306 to load the Received Signal Strength Indicator (RSSI) Buffer 962 with the constant ACTIVE 910 to indicate that a received signal has been detected.

Block 624 then directs the base microprocessor 306 to create a new record in the Log Buffer 982, the new record being assigned an array index value equal to the contents of the Index Buffer 964 and having field contents equal to the current contents of the Clk Buffer 960 and the current contents of the buffers mapped into the status word as described hereinabove in the definition of the Log Buffer 982. Thereafter, block 626 directs the base microprocessor 306 to increment the contents of the Index Buffer 964 before the RECEIVER CONTROL 936 subroutine terminates and the base microprocessor 306 is directed back to the calling routine.

Alternatively, if at block 620 the contents of the RSS Register 310 is not greater than zero, then block 628 directs the base microprocessor 306 to determine whether the contents of the Timer 956 is greater than the constant LIM 914. If not, then the base microprocessor 306 is directed back to block 618 to once again read the contents of the RSS Register 310. Alternatively, if the contents of the Timer 956 is greater than the constant LIM 914, then the RECEIVER

CONTROL 936 subroutine terminates and the base microprocessor 306 is directed back to the calling routine under the assumption that it is not productive to keep looking for a signal at the current carrier frequency.

Operation of the Base Circuit Module - SETUP RANGES Referring to Figures 10 and 16, the operation of the SETUP RANGES subroutine 938 will now be described in further detail. Generally, the SETUP RANGES subroutine 938 gives an operator the opportunity to define the monitored area in terms of a predefined boundary, a calibrated boundary, or a calibrated progression of boundary contours.

Block 640 directs the base microprocessor 306 to cause the Display Interface 324 to write to the display 20 the message, "Press 'A' for Predefined, Press 'B' for Calibration, Press 'A' & 'B' for Progression."

Block 642 then directs the base microprocessor 306 to cause the Keypad

Interface 322 to poll the keypad 18 for a user keypress action.

If the Keypad Interface 322 passes back a value corresponding to the constant A 920, then the base microprocessor 306 is directed forward to block 642. Alternatively, if the Keypad Interface 322 passes back a value corresponding to the constant B 922, then the base microprocessor 306 is directed forward to block 644. Alternatively, if the Keypad Interface 322 passes back a value corresponding to the constant A&B 924, then the base microprocessor 306 is directed forward to block 646.

Block 642 directs the base microprocessor 306 to execute the PREDEFINED RANGE subroutine 948. Upon completion of the PREDEFINED RANGE subroutine 948, the SETUP RANGES subroutine 938 terminates and the base microprocessor 306 is directed back to the calling routine.

Alternatively, block 644 directs the base microprocessor 306 to execute the CALIBRATE RANGE subroutine 946. Upon completion of the CALIBRATE RANGE subroutine 946, the SETUP RANGES subroutine 938 terminates and the base microprocessor 306 is directed back to the calling routine.

Alternatively, block 646 directs the base microprocessor 306 to execute the PROGRESSIVE RANGES subroutine 950. Upon completion of the

PROGRESSIVE RANGES subroutine 950, the SETUP RANGES subroutine 938 terminates and the base microprocessor 306 is directed back to the calling routine.

Operation of the Base Circuit Module - PREDEFINED RANGE

Referring now to Figures 10 and 17, the PREDEFINED RANGE subroutine 948 will now be described in greater detail. Generally, the PREDEFINED RANGE subroutine 948 establishes either a large, medium, or small monitored area by respectively setting a low, medium, or high received signal strength threshold. A received signal having a received signal strength below this threshold will be deemed to have been transmitted from outside of the monitored area.

Once a predefined monitored area has been selected, the PREDEFINED RANGE subroutine 948 gives the operator an opportunity to test its boundaries so that the operator can decide whether the selected predefined monitored area is suitable.

To this end, block 650 directs the base microprocessor 306 to cause the Display Interface 324 to write to the display 20 the message, "Press 'A' for maximum range, Press 'B' for medium range, Press 'A' & 'B' for minimum range."

Block 652 then directs the base microprocessor 306 to cause the Keypad Interface 322 to poll the keypad 18 for a user keypress action.

If the Keypad Interface 322 passes back a value corresponding to the constant A 920, then the base microprocessor 306 is directed forward to block 654. Alternatively, if the Keypad Interface 322 passes back a value corresponding to the constant B 922, then the base microprocessor 306 is directed forward to block 656. Alternatively, if the Keypad Interface 322 passes back a value corresponding to the constant A&B 924, then the base microprocessor 306 is directed forward to block 658.

Block 654 directs the base microprocessor 306 to store in the first element of the Range Buffer 980 the constant MAXIMUM 926. The base microprocessor 306 is then directed forward to block 660.

Alternatively, block 656 directs the base microprocessor 306 to store in the first element of the Range Buffer 980 the constant MEDIUM 928. The base microprocessor 306 is then directed forward to block 660.

Alternatively, block 658 directs the base microprocessor 306 to store in the first element of the Range Buffer 980 the constant MINIMUM 930. The base microprocessor 306 is then directed forward to block 660.

Block 660 directs the base microprocessor 306 to read the contents of the Received Signal Strength (RSS) Register 310 and block 662 directs the base microprocessor 306 to determine whether the contents of the RSS Register 310 is greater than the contents of the first element of the Range Buffer 980.

If so, then block 664 directs the base microprocessor 306 to cause the Display Interface 324 to write to the display 20 the message, "WITHIN RANGE".

Alternatively if not, then block 666 directs the base microprocessor 306 to cause the Display Interface 324 to write to the display 20 the message, "OUT OF RANGE". In either case, the base microprocessor 306 is directed forward block 668. Block 668 directs the base microprocessor 306 to cause the Display Interface 324 to write to the display 20 the message, "Press 'A' to re-test; Press 'B' to exit."

Block 670 then directs the base microprocessor 306 to cause the Keypad

Interface 322 to poll the keypad 18 for a user keypress action. If the Keypad Interface 322 passes back a value corresponding to the constant A 920, then the base microprocessor 306 is directed back to block 650. Alternatively, if the Keypad Interface 322 passes back a value corresponding to the constant B 922, then the base microprocessor 306 is directed forward to block 672.

Block 672 directs the base microprocessor 306 to load into the Range Count Buffer 978 codes representing the integer value 2. This step has the effect of purging elements beyond the first element in the Range Buffer 980 so that the monitored area has only one boundary which is defined in the first element in the Range Buffer 980. Thereafter, the PREDEFINED RANGE subroutine 948 terminates and the base microprocessor 306 is directed back the calling routine.

Operation of the Base Circuit Module - CALIBRATE RANGE

With reference now to Figures 10 and 18, the CALIBRATE RANGE subroutine 946 will be described in greater detail. Generally, the CALIBRATE RANGE subroutine 946 samples the signal strength of a series of received signals and stores the weakest signal strength sample as the first and only element in the Range Buffer 980. If the received signals correspond to transmissions from the remote station (14) at various radii from the base receiver 22, then the CALIBRATE RANGE subroutine 946 sets the boundary of the monitored area based upon the strength of signal received when the remote station (14) is located at the desired boundary. Block 680 directs the base microprocessor 306 to cause the Display Interface 324 to write to the display 20 the message, "Press 'A' when you want to finish calibration."

Block 682 directs the base microprocessor 306 to cause the Minimum RSS Buffer 977 to be loaded with the constant MINIMUM 928 to set the first iteration of received signal strength at an arbitrarily high value, subject to reduction as the remote station (14) is moved away from the base station (12) during the calibration process.

Block 684 directs the base microprocessor 306 to cause the Range Count Buffer 978 to be loaded with codes representing the integer value 2. This step has the effect of purging elements beyond the first element in the Range Buffer 980 so that the monitored area has only one boundary which is defined in the first element in the Range Buffer 980.

Block 686 directs the base microprocessor 306 to read the contents of the Received Signal Strength (RSS) Register 310.

Block 688 directs the base microprocessor 306 to determine whether the contents of the RSS Register 310 is equal to zero, if so, then block 690 directs the base microprocessor 306 to cause the Display Interface 324 to write to the display 20 the message, "Scanning ..." before directing the base microprocessor 306 forward to block 692.

Alternatively, if the contents of the RSS Register 310 is not equal to zero, then block 694 directs the base microprocessor 306 to determine whether the contents of the RSS Register 310 is less than the contents of the Minimum RSS Buffer 977. If so, then block 696 directs the base microprocessor to load the Minimum RSS Buffer 977 with the contents of the RSS Register 310 before directing the base microprocessor 306 forward to block 692. Alternatively, if the contents of the RSS Register 310 is not less than the contents of the Minimum RSS Buffer 977, then the base microprocessor 306 is directed forward to block 692.

Block 692 directs the base microprocessor 306 to check whether Keypad

Interface 322 has returned a value corresponding to the constant A 924. It should be noted that if the Keypad Interface 322 has not returned any value, then the microprocessor 306 does not wait for one.

If the Keypad Interface 322 has returned a value corresponding to the constant

A 924, then the base microprocessor 306 is directed forward to block 694 because an operator has indicated through a keypress activity at the keypad 18 that he wishes to finish the calibration process. Alternatively, the base microprocessor 306 is directed back to block 686.

Block 694 directs the base microprocessor 306 to load the first element of the Range Buffer 980 with the contents of the Minimum RSS Buffer 977 multiplied by a scaling factor, in this embodiment 0.8, to in effect nominally extend the radius of the monitored area to account for variability in the electromagnetic coupling between the remote station (14) and the base station (12).

Operation of the Base Circuit Module - PROGRESSIVE RANGES Referring now to Figures 10 and 19, the PROGRESSIVE RANGES subroutine 950 will be described in further detail. Generally, the PROGRESSIVE RANGES subroutine 948 samples the signal strength of received signals specified by an operator and stores these signal strength samples as respective elements in the Range Buffer 980. If the received signals specified by the operator correspond to transmissions from the remote station (14) at various radii from the base receiver 22, then the PROGRESSIVE RANGES subroutine 948 effectively divides the monitored area with a number of boundaries or contours specified by the operator. Block 700 directs the base microprocessor 306 to cause the Display Interface 324 to write to the display 20 the message, "Press 'A' when you want to finish; Press 'B' when you want to set a range boundary."

Block 702 directs the base microprocessor 306 to load the Range Count Buffer 978 with codes representing the integer value 1 , to in effect flush the Range Count Buffer 978.

Block 704 directs the base microprocessor 306 to read the Received Signal

Strength (RSS) Register 310.

Block 706 directs the base microprocessor to determine whether the contents of the RSS Register 310 is zero. If so, then block 708 directs the base microprocessor 306 to cause the Display Interface 324 to write to the display 20 the message, "Scanning ..." before directing the base microprocessor 306 forward to block 710.

Alternatively, if contents of the RSS Register 310 is not zero, then block 712 directs the base microprocessor 306 to cause the Display Interface 324 to write to the display 20 the message, "Signal Lock".

Block 714 then directs the base microprocessor 306 to check whether the Keypad Interface 322 has returned a value corresponding to the constant B 926. It should be noted that if the Keypad Interface 322 has not returned any value, then the base microprocessor 306 does not wait for one.

If the Keypad Interface 322 has returned a value corresponding to the constant B 926, then the base microprocessor 306 is directed forward to block 716 because an operator has indicated through a keypress activity at the keypad 18 that he wishes to set a range boundary. Alternatively, the base microprocessor 306 is directed forward to block 710. Block 716 then directs the base microprocessor 306 to store in the Range Buffer 980 as indexed by the Range Count Buffer 978 the contents of the RSS Register 310.

Block 718 then directs the base microprocessor 306 to increment the contents of the Range Count Buffer 978 before directing the base microprocessor 306 forward to block 710.

Block 710 then directs the base microprocessor 306 to check whether the

Keypad Interface 322 has returned a value corresponding to the constant A 924. It should be noted that if the Keypad Interface 322 has not returned any value, then the base microprocessor 306 does not wait for one.

If the Keypad Interface 322 has returned a value corresponding to the constant

A 924, then the base microprocessor 306 is directed back to the calling routine because an operator has indicated through a keypress activity at the keypad 18 that he wishes to end this range setting process. Alternatively, the base microprocessor 306 is directed back to block 704 to continue this range setting process.

Operation of the Base Circuit Module - LOCATE TRANSMITTER Referring now to Figures 10 and 20, the LOCATE TRANSMITTER subroutine 940 will be described in greater detail. Generally, the LOCATE TRANSMITTER subroutine 940 measures the strength of a signal received at the receiver 22 to determine the location of the remote station (14) with respect to the monitored area. Furthermore, the LOCATE TRANSMITTER subroutine 940 flags the situation where no signal whatsoever has been received from the remote station (14) for a predetermined period of time.

Block 730 directs the base microprocessor 306 to determine whether the contents of the RSSI Buffer 962 have been set equal to the constant ACTIVE 910 under the direction of the RECEIVER CONTROL subroutine 936 as an indication that a signal has been received.

If not, then block 732 directs the base microprocessor 306 to determine whether the contents of the Last Xmit Timer 958 is greater than the constant

ESCAPE TIME 916. If so, then block 734 directs the base microprocessor 306 to store in the Escaped Buffer 968 the constant ACTIVE 910 before directing the base microprocessor forward to block 736. Alternatively, if the contents of the Last Xmit Timer 958 is not greater than the constant ESCAPE TIME 916, then the base microprocessor is directed forward to block 736.

Alternatively, if at block 730 the contents of the RSSI Buffer 962 have been set equal to the constant ACTIVE 910, then block 738 directs the base microprocessor 306 to store in the Last Xmit Timer 958 the value zero. This step effectively resets the Last Xmit Timer 958 which restarts the time interval during which the next signal must be received from the remote station (14) in order for the Escaped Buffer 968 not to be set to indicate that an escape has occurred.

Block 740 then directs the base microprocessor 306 to load the Loop Buffer

966 with codes representing the integer 1. This step initializes a loop to determine the location of the remote station (14) with respect to the monitored area.

Block 742 directs the base microprocessor 306 to determine whether the contents of the Received Signal Strength (RSS) Register 310 is greater than the contents of the Range Buffer 980 indexed by the Loop Buffer 966. This test in effect determines whether the strength of the received signal is greater than the expected strength of a signal transmitted from the first boundary or contour defining the monitored area as set under the direction of the SETUP RANGES subroutine 938. If the contents of the Received Signal Strength (RSS) Register 310 is greater than the contents of the Range Buffer 980 indexed by the Loop Buffer 966, then block 744 directs the base microprocessor 306 to store in the Location Buffer 970 the contents of the Loop Buffer 966. This step records that the remote station was found to be located within the contour or boundary having an ordinal position measured from the base station (12) equal to the contents of the Loop Buffer 966. Thereafter, the base microprocessor is directed forward to block 736.

Alternatively, if the contents of the Received Signal Strength (RSS) Register

310 is not greater than the contents of the Range Buffer 980 indexed by the Loop Buffer 966, then block 746 directs the base microprocessor to increment the contents of the Loop Buffer 966. This step corresponds to a determination that the remote station (14) was found to be located outside the contour or boundary having an ordinal position measured from the base station (12) equal to the contents of the Loop Buffer 966.

Block 748 directs the base microprocessor 306 to determine whether the contents of the Loop Buffer 966 is greater than the difference of the integer 1 subtracted from the contents of the Range Count Buffer 978. If not, then there remain untested contours within which the remote station (14) may be located and the base microprocessor 306 is directed back to block 742 to continue such testing.

Alternatively, if the contents of the Loop Buffer 966 is greater than the difference of the integer 1 subtracted from the contents of the Range Count Buffer 978, then no untested contours remain and the remote station (14) must be located outside of the monitored area. Therefore, block 750 directs the base microprocessor 306 to store in the Location Buffer 970 the constant OUT OF BOUNDS 918. Block 736 directs the base microprocessor 306 to create a new record in the Log Buffer 982, the new record being assigned an array index value equal to the contents of the Index Buffer 964 and having field contents equal to the current contents of the Clk Buffer 960 and the current contents of the buffers mapped into the status word as described hereinabove in the definition of the Log Buffer 982. Thereafter, block 738 directs the base microprocessor 306 to increment the contents of the Index Buffer 964 before the LOCATE TRANSMITTER 940 subroutine terminates and the base microprocessor 306 is directed back to the calling routine.

Operation of the Base Circuit Module - DETECT TAMPERING Referring now to Figures 1 , 10 and 21 , the DETECT TAMPERING subroutine 942 will now be described in greater detail. Generally, the DETECT TAMPERING subroutine 942 monitors whether and when the base station 12 has been moved or the power input 24 or the communication connection 28 has been disconnected.

Block 760 directs the base microprocessor 306 to determine whether the contents of the Motion Register 314 are equal to the constant ACTIVE 910. If not, then the base microprocessor 306 is directed forward to block 762.

Alternatively, if the contents of the Motion Register 314 are equal to the constant ACTIVE 910, then block 764 directs the base microprocessor to store in the Motion Timer 952 the constant Timer Start 904 which has the effect of beginning an interval during which disconnecting either the power input 24 or the communication connection 28 will cause the Motion Alarm Buffer 974 to be set ACTIVE.

Block 766 then directs the base microprocessor 306 to determine whether the contents Utility Timer Buffer 954 are greater than the integer zero which would indicate that the detected motion has occurred proximately to a previous disconnection of either the power input 24 or the communication connection 28. If so, block 768 directs the base microprocessor 306 to store in the Motion Alarm Buffer 974 the constant ACTIVE 910 before directing the base microprocessor 306 forward to block 772.

Alternatively, if the contents Utility Timer Buffer 954 are not greater than the integer zero, then block 774 directs the base microprocessor 306 to store in the Motion Info Buffer 972 the constant ACTIVE 910 before directing the base microprocessor 306 forward to block 772.

Block 772 then directs the base microprocessor 306 to create a new record in the Log Buffer 982, the new record being assigned an array index value equal to the contents of the Index Buffer 964 and having field contents equal to the current contents of the Clk Buffer 960 and the current contents of the buffers mapped into the status word as described hereinabove in the definition of the

Log Buffer 982.

Thereafter, block 774 directs the base microprocessor 306 to increment the contents of the Index Buffer 964 before directing the base microprocessor 306 forward to block 762.

Block 762 directs the base microprocessor 306 to determine whether the contents of the Power Register 316 is equal to the constant ACTIVE 910. If not, then the base microprocessor 306 is directed forward to block 776 which directs the base microprocessor 306 to determine whether the contents of the

Telephone Register 318 is equal to the constant ACTIVE 910. If not, then the DETECTION TAMPERING subroutine 942 terminates and the base microprocessor 306 is directed back to the calling routine.

Alternatively, if either at block 762 the contents of the Power Register 316 is determined equal to the constant ACTIVE 910 or at block 776 the contents of the Telephone Register 318 is determined equal to the constant ACTIVE 910, then the base microprocessor 306 is directed forward to block 778.

Block 778 directs the base microprocessor 306 to store in the Utility Timer 954 the constant Timer Start 904 which has the effect of beginning an interval during which moving the base station 12 will cause the Motion Alarm Buffer 974 to be set ACTIVE.

Block 780 then directs the base microprocessor 306 to determine whether the contents of the Motion Timer 952 are greater than the integer zero which would indicate that the detected disconnection of the power input 24 or the communication connection 24 has occurred proximately to a movement of the base station 12.

If so, block 782 directs the base microprocessor 306 to store in the Motion

Alarm Buffer 974 the constant ACTIVE 910 and block 784 directs the base microprocessor 306 to store in the Utility Alarm Buffer 976 the constant ACTIVE 910 before directing the base microprocessor 306 forward to block 786.

Alternatively, if the contents of the Utility Timer Buffer 954 are not greater than the integer zero, then block 788 directs the base microprocessor 306 to store in the Utility Alarm Buffer 976 the constant ACTIVE 910 before directing the base microprocessor 306 forward to block 786.

Block 786 then directs the base microprocessor 306 to create a new record in the Log Buffer 982, the new record being assigned an array index value equal to the contents of the Index Buffer 964 and having field contents equal to the current contents of the Clk Buffer 960 and the current contents of the buffers mapped into the status word as described hereinabove in the definition of the Log Buffer 982. Thereafter, block 788 directs the base microprocessor 306 to increment the contents of the Index Buffer 964 before the DETECT TAMPERING subroutine 942 ends and the base microprocessor 306 is directed back to the calling routine.

Thus it will be appreciated that there has been disclosed a way to monitor a monitoree within a monitored area, including harnessing a closeable housing to the monitoree, the housing containing a transmitter for transmitting an identification signal for identifying the transmitter, locating within the monitored area a receiver for receiving the identification signal, measuring the signal strength of the identification signal received at the receiver, and comparing the signal strength to a predetermined signal strength threshold to determine whether the transmitter is located within the monitored area.

This way includes periodically logging data into a data log at the receiver, wherein logging data in a data log includes logging at least one of: the signal strength, data describing the state of the receiver, data describing the state of the closeable housing, and data describing the state of the harness. Furthermore, the way includes periodically uploading the data log to a server from the receiver.

Desirably, the way includes: detecting whether the receiver has been moved, connecting the receiver to receive power from electrical power mains and detecting when the receiver has been disconnected from the electrical power mains, and connecting the receiver to a communication channel to the server and detecting when the receiver has been disconnected from the communication channel. Additionally, the way includes generating an alarm signal if within a predetermined time interval the receiver has been both moved and disconnected from either the electrical power mains or the telecommunication channel. Preferably, the way includes detecting whether the closeable housing has been at least partially opened and encoding within the identification signal an indicia that the closeable housing has been at least partially opened. Thus, the step of securing to a monitoree might include: forming the harness into a loop having first and second ends, placing a limb of the monitoree through the loop, and securing the first and second ends of the loop within the closeable housing.

Similarly, the way might further include: detecting whether the harness has been modified and encoding within the identification signal an indicia that the harness has been modified. In this situation, detecting whether the harness has been modified includes detecting whether the harness has been cut or stretched whether an electrical jumper has been connected to the harness.

The way might still further include calibrating the predetermined signal strength threshold, for example by selecting one of a set of preset values or by first locating the transmitter at a boundary of the monitored area and then setting the predetermined signal strength threshold equal to the signal strength or the signal strength multiplied by a scaling factor. By extension, one might calibrate a set of predetermined signal strength thresholds by: locating the transmitter at successive distances from the receiver, and setting members of the set of predetermined signal strength thresholds equal to the signal strengths corresponding to the locating the transmitter at respective successive distances from the receiver.

While specific embodiments of the invention have been described and illustrated, such embodiments should be considered illustrative of the invention only and not as limiting the invention as construed in accordance with the accompanying claims.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method comprising:

(a) securing to a monitoree by a harness a closeable housing containing a transmitter for transmitting an identification signal for identifying the transmitter;

(b) locating within a monitored area a receiver for receiving the identification signal;

(c) measuring the signal strength of the identification signal received at the receiver; and

(d) comparing the signal strength to a predetermined signal strength threshold to determine whether the transmitter is located within the monitored area.

2. A method as claimed in Claim 1 , further including at the receiver periodically logging data into a data log.

3. A method as claimed in Claim 2, wherein logging data in a data log includes logging at least one of:

(a) the signal strength;

(b) data describing the state of the receiver;

(c) data describing the state of the closeable housing; and

(d) data describing the state of the harness.

4. A method as claimed in Claim 3, further including at the receiver periodically uploading the data log to a server.

5. A method as claimed in either Claim 1 or Claim 3, further including detecting whether the receiver has been moved.

6. A method as claimed in either Claim 1 or Claim 3, further including:

(a) connecting the receiver to receive power from electrical power mains; and (b) detecting when the receiver has been disconnected from the electrical power mains.

7. A method as claimed in Claim 6, further including detecting whether the receiver has been moved.

8. A method as claimed in Claim 7, further including generating an alarm signal if within a predetermined time interval the receiver has been both moved and disconnected.

9. A method as claimed in either Claim 1 or Claim 3, further including:

(a) connecting the receiver to a communication channel to the server; and

(b) detecting when the receiver has been disconnected from the communication channel.

10. A method as claimed in Claim 9, further including detecting whether the receiver has been moved.

11. A method as claimed in Claim 10, further including generating an alarm signal if within a predetermined time interval the receiver has been both moved and disconnected.

12. A method as claimed in either Claim 1 or Claim 3, further including:

(a) detecting whether the closeable housing has been at least partially opened; and

(b) encoding within the identification signal an indicia that the closeable housing has been at least partially opened.

13. A method as claimed in Claim 12, wherein securing to the monitoree includes:

(a) forming the harness into a loop having first and second ends;

(b) placing a limb of the monitoree through the loop; and

(c) securing the first and second ends of the loop within the closeable housing.

14. A method as claimed in either Claim 1 or Claim 3, further including:

(a) detecting whether the harness has been modified; and

(b) encoding within the identification signal an indicia that the harness has been modified.

15. A method as claimed in Claim 14, wherein detecting whether the harness has been modified includes detecting whether the harness has been cut.

16. A method as claimed in Claim 14, wherein detecting whether the harness has been modified includes detecting whether the harness has been stretched.

17. A method as claimed in Claim 14, wherein detecting whether the harness has been modified includes detecting whether an electrical jumper has been connected to the harness.

18. A method as claimed in Claim 1 , further including calibrating the predetermined signal strength threshold.

19. A method as claimed in Claim 18, wherein calibrating the predetermined signal strength threshold includes selecting one of a set of preset values.

20. A method as claimed in Claim 18, wherein calibrating the predetermined signal strength threshold includes:

(a) locating the transmitter at a boundary of the monitored area; and

(b) setting the predetermined signal strength threshold equal to the signal strength.

21. A method as claimed in Claim 20, wherein calibrating the predetermined signal strength threshold includes setting the predetermined signal strength threshold equal to the signal strength multiplied by a scaling factor.

22. A method as claimed in Claim 20, further including calibrating a set of predetermined signal strength thresholds by:

(a) locating the transmitter at successive distances from the receiver; and

(b) setting members of the set of predetermined signal strength thresholds equal to the signal strengths corresponding to the locating the transmitter at respective successive distances from the receiver.

23. An apparatus comprising:

(a) a transmitter for transmitting an identification signal;

(b) a closeable housing enclosing the transmitter, the housing having first and second opposite ends; and

(c) an elongated and electrically conductive harness having first and second ends, the first and second ends being transversely receivable into the first end of the housing for engagement by the housing and electrical connection to the transmitter when the housing is in a closed state, whereby the harness is configurable into a loop for securing the housing.

24. An apparatus as claimed in Claim 23, further including:

(a) a harness-tamper voltage detector for detecting a potential difference between the first and second ends of the harness; and

(b) a harness-tamper signal generator for generating a harness-tamper signal in response to the harness-tamper voltage detector detecting a change in potential difference greater than a predetermined threshold.

25. An apparatus as claimed in Claim 23, wherein:

(a) the first end of the harness supports a perpendicular spur; and (b) the spur is receivable into the second end of the housing for engagement by the housing and electrical connection to the transmitter when the housing is in the closed state.

26. An apparatus as claimed in Claim 25, further including:

(a) a housing-open voltage detector for detecting a potential difference between the first end and the spur of the harness; and

(b) a housing-open signal generator for generating a housing-open signal in response to the housing-open voltage detector detecting a change in potential difference greater than a predetermined threshold.

27. An apparatus as claimed in Claim 23, further including a lock-bolt receivable into the closeable housing to secure the closeable housing in the closed state.

28. An apparatus as claimed in Claim 27, further including a key receivable into the lock-bolt and the first end of the harness to secure the lock-bolt to the first end of the harness, whereby the lock-bolt cannot be removed from the housing while secured to the first end of the harness.

29. An apparatus as claimed in Claim 28, wherein the lock-bolt and the key further include cooperating members for securing the key to the lock- bolt.

30. An apparatus as claimed in Claim 29, wherein the cooperating members on the key include:

(a) a broad head; and

(b) a catch.

31. An apparatus as claimed in Claim 30, wherein the key further includes a breakaway joint located between the broad head and the catch such that the broad head is separable from the catch, whereby the key may be removed from the lock-bolt and the first end of the harness.

32. An apparatus comprising:

(a) a receiver for receiving an identification signal transmitted by a transmitter, the receiver including:

(i) a signal strength detector for detecting the strength of the identification signal received at the receiver; and

(ii) a comparator for comparing the signal strength to a predetermined signal strength threshold to determine whether the transmitter is located within a predetermined monitored area.

33. An apparatus as claimed in Claim 32, further including a motion detector for generating a motion signal when the apparatus has moved.

34. An apparatus as claimed in Claim 33, further including:

(a) a power connector for connecting the apparatus to receive power from electrical power mains; and

(b) an electricity detector for generating a disconnection signal when the apparatus has been disconnected from the electrical power mains.

35. An apparatus as claimed in Claim 33, further including:

(a) a communication connector for connecting the apparatus to a communication channel; and

(b) a channel detector for generating a disconnection signal when the apparatus has been disconnected from the communication channel.

36. An apparatus as in either Claim 34 or Claim 35, further including an alarm for generating an alarm condition when the apparatus has been both moved and disconnected within a predetermined time interval.

37. An apparatus as claimed in Claim 36, further including a data-logger for periodically logging in a data log at least one of:

(a) the signal strength; (b) the motion signal; and

(c) the disconnection signal.

38. An apparatus as claimed in Claim 32, wherein the comparator is adapted to compare the signal strength to a set of predetermined signal strength thresholds to determine whether the transmitter is located within one of a set of predetermined monitored areas.

39. A system comprising:

(a) the apparatus as claimed in Claim 32; and

(b) the apparatus as claimed in Claim 23, wherein the apparatus as claimed in Claim 23 is the transmitter transmitting the identification signal to the receiver for receiving an identification signal transmitted by a transmitter as claimed in Claim 32.