US3852740A

US3852740A - Alarm system with radio alarm link and equipment-activating power line link

Info

Publication number: US3852740A
Application number: US00351164A
Authority: US
Inventors: I Haymes
Original assignee: Individual
Current assignee: Individual
Priority date: 1973-04-16
Filing date: 1973-04-16
Publication date: 1974-12-03
Anticipated expiration: 1991-12-03

Abstract

An alarm system has both radio and power line communication links between the protected premises and a monitoring station. Intrusion alarm monitoring equipment at the monitoring station is activated to respond to radio alarm signals from the protected premises by ''''activate'''' signals that originate at the protected premises and are transmitted over power lines to the monitoring station. The monitoring station signals back to the protected premises over the power lines the fact that it is ''''armed'''' or activated as to intrusion alarm signals from those premises, and also signals any intrusion alarm detected at said protected premises. The intrusion alarm transmitter or transmitters at the protected premises can send a radio alarm signal only in compliance with current F.C.C. requirements.

Description

llnited States Patent 1191 1111 3,852,740

Haymes Dec. 3, 1974 [54] ALARM SYSTEM WITH RADKO ALARM 3,757,315 0 1073 Birchficld c 111. 340 224 LINK AND EQUlPMENT-ACTWATING POWER LINE LINK Primary Examiner-Glen R. Swann, Ill

' Attorney, Agent, or Firm-Oltman and Flynn [75] Inventor: Irving Haymes, Tamarac, Fla. Y

[73] Assignees: Earl Yale Fine; Kenneth Borzage; ABSTRACT S0ley Goldberg; Steven Fine, part An alarm system has both radio and power line comnte est o ch munication links between the protected premises and [22] Filed: AP 16, 1973 I a monitoring station. Intrusion alarm monitoring equipment at the monitoring station is activated to respond to radio alarm signals from the protected prem- [21] Appl. No.: 351,164

ises by activate signals thatoriginate at the pro- [52] US Cl 340/416 340/224 340/310 R tected premises and are transmitted over power lines g 340/420 to the monitoringstation. The monitoring station sig- 51 1111. C1. G08b 25/00 back the Pmtected premises the Power [58] Field of searchm 340/224 416 420 310 R lines the fact that it is armed or activated as to' in- 54 1 27 trusion alarm signals from those premises, andalso signals any intrusion alarm detected at said protected [56] I References Cited premises]. The tmtrugion alarm transmiter or granslmiters a 6 pro 60 e premises can sen a ra 10 a arm UNITED STATES PATENTS signal only in compliance with current F.C.C. require- 1,698,770 1 1929 0111 340/310 R mems 2,003,877 6/1935 Blatterman... 340/310 R 2,547,024 4/1951 Noble 340/310 R 20 ClalmS, 3 Drawing Flames 3,540,043 11/1970 Crosthwait 340/224 g "3'X-ALARMDEC0DERS. 2 i l ALARM *7;

o ALER.

gggg J EMERGENCY 2? AuoIaEALAm:

' L DISTRIBUTION M r PANEL. I i FIRE. i-- 1 l 0 -71 ALARM. 1 i INHIBIT l l I j l ACTIVATE I KEY 1 i 1 F- TRANSMITTER. l i 9 L2! 22 I 1 7 W l L action/001711110 STATION.

,- i I I POLARITY 1 I REVERSER. 5 i I 24 2: FI/F2 I ii'f'iron. I I6- KEY PLUG. I5 KEY JACK, L I 1 1a In 1 i I PULSE l OSCILLATOR. I7 L? i i 1 i|.l|lli 12 14 .42 I3 I 1 1 1 11 WINDOWALARM 00m ALARM 3 gffggf FIRE ALARM TRANSMITTER. TRANSMITTER. TRANSMITTER TRAAGMITTER. 1 1 1 1 1 a L L l I I0 PROTECTED PREMISB.

PATENTEL DEC 31974 sum 1 or 2 ALARM DECODERS.

POLICE DEPT FIRE DEPT AUTO. DIAIER.

AUDIBLE KZ'ARM.

LN 7/ ALARM.

ALARM DETECTION 8 DISTRIBUTION PANEL.

BURGLARK EMERGENCY FIRE.

INDICATOR 8 BELL TRANSMITTER.

INHIBIT RADIO RECEIVER.

KEY RECEIVER.

ACTIVATE J R. mm AT w W 5 M R L R. L N o 0 E m m H mm m F FT m Rn ma 0 mx us CO PO f V'- 1 m n m; Q m m E I I M H H M\| mwwm 4 K R a M M: W 4 4| EAm Mm mx kfl m R mm M. 2 W RM a mm m a J 1 R m. mm L Mm F IIL L IO PROTECTED PREMISES.

PATENIEL 3W 3,852,740

sum 20F 2 SELECTIVE CARRIER DE MODULATOR. LIMI TE R.

FROM AMPLIFIER. mIIgER I i I I I 2 g 2 -54 II\K I F2 DECODER l g 3 3 Q 59 i I 64 I 1 58 *W'I' fi 1 l 55 I I $2127 I I e3 E2 I 65 61x c g I MODULE. 1 I

I' I' IT 0 T 85 5x33557 01; OSCILLATOR.

ALARM SYSTEM WITH RADIO ALARM LINK AND EQUIPMENT-ACTIVATING POWER LINE LINK SUMMARY OF THE INVENTION This invention relates to an alarm system for responding to various types of alarm conditions, particularly in an industrial plant, a museum or other public building, or a private estate, condominium, apartment building, or house where security from burglars, fire or other hazards is particularly important.

In broad outline, the present system has radio alarm transmitters at or near the premises to be protected from intrusion and intrusion alarm monitoring equipment at a different location which, for purposes of this discussion, may be called the security headquarters. The monitoring equipment is conditioned to respond to intrusion alarm signals at the protected premises by an action initiated there by a custodian. For example, at the end of the workday in an industrial plant all the doors and windows may be closed, and from then until the beginning of the next workday they should remain closed. During this time period when nobody would open a door or window except an unwelcome intruder, the system should be activated to detect such intrusions and it is the custodians responsibility to do this. The

present system has provision for activating the intrusion alarm monitoring equipment at the security headquarters by signals transmitted over power lines from the premises to be protected. Also, this system has provision for signalling back over the power lines from the security headquarters the fact thatthe system has been activated for intrusions at those premises or that a door or window is open there, so that the custodian will be so informed. Also, the security headquarters automatically notifies the custodian over the power lines whenever an intrusion alarm condition occurs at his premises. The window and door alarm transmitter or transmitters in the present system have a tamper-proof arrangement for insuring that these transmitters comply with current F.C.C. regulations governing the duration of intermittent fon" and off" broadcast intervals.

It is a'principa l object of this invention to provide a novel'and improved alarm system.

Another object of this invention is to provide such an alarm system which has both a radio link and a power line link between the premises to be protected and a station where alarm monitoring equipment is located.

Another object of this invention is to provide a hybrid alarm system with both radio and power line links which has all the versatility of previous all-wire alarm systems.

Another object of this invention is to provide such an alarm system in whichv the power line link is used to activate the equipment at the monitoring station to respond to intrusion alarm signals from the protected premises, and to signal back to the protected premises that such activation has occurred.

Another object of this invention is toprovide such an alarm system in which the power line link is used to signal from the monitoring station back to the protected premises when an alarm condition has occurred at said protected premises.

Another object of this invention is to provide a novel and improved alarm system having a radio alarm link with provision for insuring that the intrusion alarm signal transmissions comply with current F.C.C. requirements.

Further objects and advantages of this invention will be apparent from the following detailed description of a presently-preferred embodiment that is described with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 illustrates the present alarm system schematically, primarily in block diagram form;

FIG. 2 is a circuit diagram of equipment at the monitoring station in FIG. 1 for receiving coded signals coming over power lines from the protected premises; and

FIG. 3 is a circuit diagram showing schematically a burglar alarm transmitter at the protected premises in the present system.

DESCRIPTION OF THE PREFERRED EMBODIMENT OVERALLSYSTEM FIG. 1

Referring to FIG. 1, at the protected premises 10 are located one or more window alarm transmitters 11, which transmit a distinctively modulated radio signal whenever a window is open there, and one or more door alarm transmitters 12, which transmit a distinctively modulated radio signal whenever a door is open there. These window and

door alarm transmitters

11 and 12 are described in more detail hereinafter with reference to FIG. 3. In some situations, a single transmitter may transmit both window alarms and door alarms.

Also located at the protected premises are one or more fire alarm transmitters 13, which broadcast a distinctively modulated radio signal whenever a tire is detected, and one or more emergency alarm transmitters 14, which broadcast a distinctively modulated radio signal whenever a'particular type of emergency occurs on the premises, such as a malfunction of refrigerators or freezers in a food store, for example, or a signal purposely initiated by a person in need of help.

The carrier frequency is the same for all the different types of radio alarm signals. The modulation for door alarms may be the same as for window alarms, since both indicate a burglary or they may be different. The respective modulations for emergency alarms and fire alarms are different from each other and from the door and window alarms since each calls for a different type of response.

Also located at the protected premises is a key jack 15 for receiving a portable key plug 16 carried by a custodian. The key jack 15 is connected to an oscillator 17 which produces pulses at a frequency F l or at a different frequency F2, as explained hereinafter. The oscillator l7 pulse-modulates a carrier signal oscillator 18, whose output is connected through a conventional wall socket (not shown) to a volt power line 19.

For the sake of simplicity, this power line 19 is shown connected directly to the monitoring station 20 of the present system, which is remote from the protected premises and which may serve a number of different protected premises. However, it is to be understood that this simplified, direct power line connection might will be transmitted over power lines from the protected premises to the monitoring station 20.

At the monitoring station, the pulse-modulated carrier signal coming from the protected premises 10 operates a key receiver 21 which will determine from this incoming signal whether or not the burglar alarm monitoring equipment at the monitoring station should be armed" as to those protected premises (i.e., activated or conditioned to respond to various door or window alarm conditions that may occur at those protected premises).

The key receiver 21 controls a transmitter 22 at the monitoring station whose output is connected to a conventional wall power socket there to send a signal over the power lines 19 back to a decoder 23 at the protected premises 10. The out-put from this decoder is a DC. signal whose plurality is reversed by a polarity reverser 24 before being applied to terminal 25 of the key jack 15, which is engaged by a corresponding terminal 26 on the key plug 16 when the latter is inserted in the key jack. When such insertion is made, another terminal 27 on a key plug contacts the grounded key jack terminal 28.

A light emitting diode 29 in the key plug is connected across

terminals

26 and 27 to be energized by the decoded signal coming back over the power lines from the transmitter 22 at the monitoring station such that:

1. if a continuous, unmodulated carrier signal is received from the monitoring station transmitter 22, the light emitting diode 29 will be on continuously;

2. if the carrier signal received from the transmitter 22 is pulse modulated, the light emitting diode 29 will flash on and off, which indicates that the protected premises 10 are not secure, such as due to a door or window being open; and

3. if no carrier signal is received from the monitoring station transmitter 22, the light emitting diode will be off, which indicates that the entire burglar alarm system is disarmed for these protected premises.

Also, a horn, buzzer or other audible warning device (not shown) may be connected to a suitable decoder plugged into any power outlet at the protected premises to sound an alarm at the protected premises only if the carrier signal from the monitoring station transmitter 22 is pulse-modulated.

The monitoring station also has a radio receiver 30 which receives the alarm signals transmitted by any of the alarm transmitters 11-14 at any protected premises 10. The incoming radio-transmitted alarm signal is applied to alarm decoders 31 which may differentiate among the emergency, fire and window or door (burglary) radio alarm signals. In one practical embodiment, each decoder is a Signetics tone decoder phase locked loop, Model SE/NE 567, as disclosed in the product manual of Signetics Corporation, copyright 1972, pages 219-228.

The decoded alarm signal is applied to an alarm detection and distribution panel 32 at the monitoring station, one of whose functions is to signal an appropriate recipient that a predetermined alarm condition has occurred at the protected premises 10. For example, the police may be notified of a door-open or window-open alarm condition, and the fire department may be notified of a fire alarm condition at these premises. A private security service may be notified by telephone through an automatic dialer that an emergency alarm condition has occurred at the protected premises. In one practical embodiment, the alarm detection and distribution panel 32 is a Model 12-240 alarm, manufactured by Design Controls, Inc., 111 Cantiague Rock Road, Westbury, N. Y. 1 1590, and shown in that companys drawing no. 500-541, revision E, dated Aug. 4, 1971, and supplied to installers of such alarms, including applicant, prior to the filing date of the present application.

The monitoring station 20 is armed, or activated, as to a particular protected premises 10 by turning on circuitry in the panel 32 to signal the police and to operate the automatic dialing equipment and the audible alarms. Preferably, the monitoring station 20 is armed continuously at all times for emergency and fire alarms from the protected premises, and the alarm signalling for such conditions is not under the control of the custodians key plug 16.

PROTECTED PREMISES Referring again to the equipment at the protected premises 10 in FIG. 1, when the key plug 16 is inserted into the key jack 15, an end terminal 33 on the key plug engages a spring-contact terminal 34 on the key jack which is connected to a control terminal 17a of the pulse oscillator 17. A pair of

resistors

35 and 36 in the key plug are connected between its end terminal 33 and the terminal 27 which is grounded when the key plug is inserted into the key jack. The juncture 37 between

resistors

35 and 36 is connected to the mobile contact 38 of a manually operable switch in the key plug. This switch has a fixed contact 39 that is connected directly to terminal 27. When

switch

38, 39 is closed it shorts out resistor 36.

Switch

38, 39 is a normally-open switch that returns to its open condition as soon as its manually operated actuator is released.

The key jack has a normally-

open switch

40, 41 with a fixed contact 41 that is grounded and a mobile contact 40 that is connected to the negative terminal of a battery 42. The mobile switch contact 40 is suitably coupled mechanically to the key jack terminal 34 through an electrically insulating coupling designated schematically by the dashed line 43, such that

switch

40, 41 closes when the key plug 16 is inserted into the key jack 15.

All of the alarm transmitters 11-14 at the protected premises are energized at all times, irrespective of whether the key'plug 16 is in the key jack for those premises. Therefore, each of these transmitters is ready continuously to transmit an alarm signal to the monitoring station at all times. As already stated, the monitoring station 20 is armed at all times to respond to emergency and fire alarm signals from the protected station, but it is armed to respond to intrusion alarm signals only after the key plug 16 is inserted in the key jack 15 at those premises.

The pulse oscillator 17 at the protected premises is an intergrated circuit of known design that is capable of generating pulses at different frequencies, depending upon the voltage at its control terminal 17a. In the present system, this control voltage at terminal 1711 may have either of two values, and the output pulse frequency of the oscillataor may be either of two values, F1 or F2.

The positive terminal of battery 42 is connected to a second terminal 17b of the pulse oscillator to provide the power supply for this oscillator when

switch

40, 41

in the key jack is closed. The voltage at the firstmentioned terminal 17a of this oscillator determines its pulse frequency, and this voltage depends 1 upon whether or not the resistor 36 is shorted out. Thus, with key plug 16 inserted into the key jack 15 and the

manual switch

38, 39 in the key plug open, the oscillator terminal 170 will be connected to ground through the series-connected resistors 35 and 36., and its voltage will be at the higher of two values, and the pulse oscillator frequency will be F1. However, when the

manual switch

38, 39 in the key plug is closed, the oscillator terminal 17a will be connected to ground through resistor 35 only (resistor 36 being short-circuited), and its voltage will be at the lower of two values, and the pulse oscillator frequency will be F2.

KEY RECEIVER AT MONITORING STATION FIG. 2 illustrates schematically important components of the key receiver 21 at the monitoring station 20. The pulse-modulated carrier signal from the protected premises It) comes in over the power lines 19 to a selective carrier amplifier 50, which amplifies this carrier, and then isdemodulated in a demodulator 51 and limited in a limiter 52 before being applied to one or more similar key detecting blocks Ka, Kb, Kc, etc., one for each different protected premises in the system.

The key detecting block Ka for the particular protected premises It) in FIG. I is shown as comprising two frequency sensitive decoders, an F1 decoder 53 and an F2 decoder 54. Each of these decoders is an integrated circuit with eight terminals, terminal 3 being the input terminal and terminal 8 being an output terminal. Each decoder is the solid stateequivalent of a reed relay, responding only to a particular frequency, F1 or F2. Each decoder may be a Signetics Corporation Model SE/NE 567 decoder, as already referred to.

Terminal 8 of the F1 decoder 53 is connected through a resistor 55 to the positive terminal of a battery 56 and is connectedthrough a capacitor 57 to the grounded negative terminal of this battery. Terminal 8 of the F1 decoder is connected through a resistor 58 and diode 59 to terminal 1 of the F2 decoder 54. Normally, terminal 8 of the F1 decoder and terminal 1 of the F2 decoder are at the positive battery voltage, and this inhibits the F2 decoder 54 from responding to an F2 signal. However, when the F1 decoder receives an F1 signal, the voltage at its terminal 8 drops to zero, as does the voltage at terminal 1 of the F2 decoder 54, so that now the F2 decoder is no longer inhibited and it can respond to an F2 input signal at its terminal 3. Such an F2 input signal at terminal 3 of decoder 54 produces a signal at its output terminal 8 that operates a sequential relay (not shown) for arming the monitoring station '20 as to intrusion alarm signals from these premises by turning on power supplies for circuits in panel 32 for police signalling, operating the automatic dialer, and sounding audible alarms. This sequential relay is energized by the first signal it receives from the F2 decoder, and it is deenergized by the next signal it will receive from the F2 decoder, as described hereinafter.

With this arrangement, to arm, or activate, the system as to intrusion alarm signals from these protected premises, the monitoring station must receive over the power lines 19 from the protected premises the carrier pulse-modulated by F1 and then the same carrier pulsemodulated by F2, and in that order (Fl preceding F2).

Otherwise, the F2 decoder 54 will remain inhibited, and the system arm relay will not be energized.

The F1 decoder 53 at the monitoring station has a narrow pass-band whose center frequency is determined by the values of a capacitor 60, an adjustable re'-- sistor 61, and a resistor 62 which is part of a key code module 63.

Similarly, the F2 decoder 54 has a narrow pass band whose center frequency is determined by a capacitor 64, an adjustable resistor 65, and a resistor 66 which also is part of the key code module 63.

The key code module 63 correspondsto the pulse frequencies F1 and F2, whichare assigned to only one protected premises, as determined by the

resistors

35 and 36 in the key plug 16 for those premises. Therefore, each key code module 63 at the monitoring station is frequency-matched to a particular key plug for a certain protected premises.

Each of the other key detecting blocks Kb, 'Kc, etc., has circuitry identical to that of the block Ka, except that the resistors in-the respective key code modules are different, so that each block Kb, Kc, etc. is frequency-tuned to only the two different modulating frequencies, F1 and F2, that are assigned to a particular protected premises. The carrier signals coming over the power lines from the different protected premises are all at the same frequency.

Resistor 55 and capacitor 57 provide a time-delay circuit for preventing the F2 decoder 54 from being inhibited again until about 250 milliseconds after the F1 input signal disappears from the F1 decoder 53. This is ample time for the F2 decoder 54 to respond to the F2 signal and energize the sequential relay for panel 32.

When the system is to be armed to respond to the window and door alarm transmitters at a particular protected premises, the

key plug switch

38, 39 is open when the key plug 16 for those premises is inserted into the key jack 15, so that the carrier signal transmitted from these protected premises will be modulated first by the F1 pulses. Then, when the

key plug switch

38, 39 is closed momentarily, this carrier will now be modulated by the F2 pulses, so as to operate the system arm relay through the F2 decoder 54. However, as already explained, this action can take place only if the F2 pulses have been preceded by the F1 pulses. The

key plug switch

38, 39 re-opens automatically when released manually, so asto re-transmit the Fl-modulated carrier to the key receiver 21 and thereby condition the F2 decoder in the key receiver to respond to the F2 modulation signal the next time the

key plug switch

38, 39 is closed.

If all the doors and windows at the protected premises are closed when the foregoing action takes place, then none of the door and

window transmitters

11 and 12 will broadcast an intrusion alarm signal to the receiver 30 at the monitoring station. However, if at this time there is an open window or door at the premises to be protected, the monitoring station cannot be armed or activated as to those premises until this condition is corrected. Also, a distinctive signal will be transduce an inhibit" signal on line 70 (FIG. 1) that is applied to terminal 1 of the F2 decoder 54 in the key receiver 21, so as to prevent the F2 decoder from responding to the FZ-pulse modulated carrier transmitted from the premises over the power lines 19 to the monitoring station. Consequently, the monitoring station cannot now be armed to respond to intrusion alarm signals from these premises.

The instruction alarm signal received by the receiver 30 at the monitoring station also causes panel 32 to produce on line 71 a signal that is applied to the transmitter 22 to cause the latter to transmit a pulsemodulated carrier over the power lines 19 back to the premises 10 which, after being decoded, produces an intermittent flashing of the light emitting diode 29. This is a visual signal to the custodian that there is a door or window open at these premises.

When all the doors and windows have been closed, the custodian closes the

key plug switch

38, 39, and the system will become armed as to these premises, as described.

When such arming takes place, the alarm signal on line 71 is removed and the transmitter 22 at the monitoring station sends a continuous carrier signal over the power lines 19 back to the premise 10. This carrier, after being decoded, is applied to the light emitting diode 29 to provide continuous illumination, which tells the custodian that the system is armed as to these premises and that no intrusion alarm condition exists there.

If, after the monitoring station has been armed as to these premises, an intrusion alarm signal is transmitted to the receiver 30 at the monitoring station, it will produce on line 71 a pulse modulation control signal to cause the light emitting diode to flash on and off again.

When the custodian wants to disarm" the system as to intrusion alarm signals originating at these premises 10 (such as at the beginning ofa work day in an industrial plant), first he closes the

key plug switch

38, 39 to again apply the F2 modulation to the carrier that is transmitted from the premises 10 over the power lines 19 to the monitoring station 20. The resulting output signal at terminal 8 of the F2 decoder 54 in the key receiver 21 energizes the sequential relay so as to remove the power for the circuits in panel 32 that signal the police, the automatic dialer and the audible alarms in the event of an intrusion alarm. Then the custodian removes the key plug from the key jack.

DOOR OR WINDOW ALARM TRANSMITTER FIG. 3

FIG. 3 illustrates schematically a door/or window alarm transmitter at the protected premises 10 in FIG. 1. There may be a single transmitter for all doors and windows to be monitored at these premises, or a single transmitter for all windows and a single transmitter for all doors there, as shown in FIG. 1, or various other- I combinations of transmitters for different windows and doors at these premises.

This transmitter complies with the current F.C.C. requirement that the broadcast interval be not longer than I second. and followed by a silent period of 30 seconds or more.

In FIG. 3 the transmitter is shown under the control of three series-connected sensor switches 80, 81 and 82, each associated with a respective door or window,

and each closed whenever that door or window is closed. Any desired number of such series-connected sensor switches may control a particular alarm transmitter. I

The sensor switches are connected in series between ground and the base of transistor Q1, whose emitter is grounded and whose collector is connected directly to the base of a second transistor Q2. The emitter of O2 is connected directly to the positive terminal of a battery B and also is connected to the base of 01 through a resistor 83.

The collector of O2 is connected through a seriesconnected diode 84 and capacitor 85 to the base of Q1. A resistor 86 is connected between ground and the juncture between diode 84 and capacitor 85.

The collector of Q2 is connected to the input of an encoder modulator 87 whose output is connected to an RF. oscillator 88 coupled to a broadcast antenna 89.

In the operation of this transmitter, as long as all of the sensor switches 80, 81 and 82 remain closed, both transistors Q1 and Q2 will remain off.

Whenever any one of the sensor switches 82 is opened, the base current of transistor Q1 turns on, causing current to flow from the collector to the emitter of 01. This turns on the base current in transistor Q2, and the resulting emitter-collector current in Q2 operates the encoder modulator 87 so that the antenna 89 broadcasts a coded, amplitude-modulated radio signal that identifies this window/door alarm transmitter at these particular protected premises. Preferably, the carrier frequency of this radio signal is about 300,000,000 Hz, and the modulation signal frequency is in the supersonic range. This radio signal will be picked up by the receiver 30 at the monitoring station (FIG. 1).

This coded signal transmission lasts only 1 second or less each time. During this 1 second or less, the capacitor will become charged through diode 84 enough to turn off the base current in Q1, thereby turning off Q1 and then turning off Q2. Capacitor 85 discharges through resistor 86, and the time constant provided by these circuit elements is such that Q1 and Q2 remain off for thirty seconds or more. At the end of this period, transistors Q1 and Q2 will turn on again (if one of the sensor switches 80-82 is still open) for the l second-orless on interval, and then they will turn off again for the 30-second-or-more off period. During this off period, a repeated opening and closing of any of the sensor switches 80-82 will have no effect. Instead the transmitter will remain off for the full period of 30 seconds or more, so as to insure compliance with the F.C.C. requirement mentioned hereinbefore.

The receiver 30 at the monitoring station includes suitable circuitry for retaining the intermittentlybroadcast signal during the alarm transmitters off periods.

It is to be understood that various modifications may be made in the system disclosed without departing from its'essential principles.

I claim:

1. In an alarm system having:

a monitoring station with alarm monitoring equipa protected premiseswhich is interconnected with the monitoring station through electrical power lines;

a radio link comprising one or more radio transmitters at the protected premises for transmitting an intrusion alarm signal when an intrusion alarm condition is detected there, and a radio receiver at the monitoring station for receiving said radio alarmsignals and operatively coupled to said alarm monitoring equipment to actuate the latter when a radio alarm signal is received;

and a power line link comprising means selectively operable at the protected premises for transmitting over power lines to the monitoring station signals for activating the alarm monitoring equipment there to respond to intrusion alarm signals broadcast from the protected premises;

the improvement wherein said power line link further comprises means at the monitoring station for transmitting over power lines to the protected premises signal information as to whether the alarm monitoring equip ment there is activated to respond to intrusion alarm signals broadcast from said protected premises.

2. An alarm system according to claim 1, wherein said transmitting means at the monitoring station is operative to transmit over power lines to the protected premises a distinctive signal which tells that an intrusion alarm condition exists at said protected premises.

3. An alarm system according to claim 1, and further comprising signal indicator means at the protected premises for responding to the power line signal coming from the monitoring station.

4. An alarm system according to claim 3, and further comprising:

means for modifying said last-mentioned signal when the radio receiver at the monitoring station receives an intrusion alarm signal from said protected premises.

5. An alarm system according to claim 4, wherein said transmitting meansat the monitoring station transmits a distinctive carrier signal over the power lines to said protected premises which is unmodulated in the absence of an intrusion alarm signal received from said protected premises and which is modulated when such reception occurs;

and said means at the protected premises for responding to said last-mentioned signal produces different indications for unmodulated and modulated signals, respectively.

6. In an alarm system having:

a monitoring station with alarm monitoring equipment; v

a protected premises which is interconnected with the monitoring station through electrical power lines;

a radio link comprising one or more radio transmitters at the protected premises for transmitting on intrusion alarm signal when an intrusion alarm condition is detected there, and a radio receiver at the monitoring station for receiving said radio alarm signals and operatively coupled to said alarm monitoring equipment to actuate the latter when a radio alarm signal is received; 7

the improvement wherein said selectively operable means at the protected premises comprises;

means for applying a carrier signal to the power lines to be transmitted to the monitoring station; 5 means for modulating said carrier signal at either of two different frequencies; and selectively operable means for activating said modulating means and for selecting the modulating frequency.

7. An alarm system according to claim 6, and further comprising means at the monitoring station for receiving the modulated carrier signal coming over the power lines from said protected premises and for responding separately to the two different modulating frequencies to condition the alarm monitoring equipment at the monitoring station to respond to intrusion alarm signals broadcast by radio from said protected premises.

8. An alarm system according to claim 7, wherein said means for responding separately to the two different modulating frequencies is sensitive to the sequence in which said two different modulating frequencies are transmitted over the power lines from said protected premises to the monitoring station.

9. An alarm system according to claim 8, wherein said means for responding separatelyto the two different modulating frequencies comprises;

a first decoder that is sensitive substantially only to a first modulating frequency, F1;

a second decoder that is sensitive substantially only to a second modulating frequency, F2;

means coupled to the output of said second decoder for conditioning the alarm monitoring equipment at the monitoring station to respond to intrusion alarm signalsfrom said protected premises in re sponse to the activation of the second decoder by an incoming F2 signal;

and circuit means interconnecting said first and second decoders for inhibiting the second decoder from being activated by an incoming F2 signal until after said first decoder has received an F1 signal.

and selectively operable means at the protected premises for transmitting signals over the power lines to the monitoring station to activate the monitoring equipment there to respond to intrusion alarm signals from the protected premises;

the improvement which comprises:

a transmitter at the monitoring station for transmitting a signal over the power lines to the protected premises when the alarm monitoring equipment at the monitoring station is conditioned to respond to intrusion alarm signals from the protected premises;

and means at the protected premises for responding to said last-mentioned signal. 12. An alarm system according to claim 11, and further comprising:

means for modifying said last-mentioned signal when the alarm monitoring equipment responds to an intrusion alarm signal from said protected premises.

13. An alarm system according to claim 12, wherein said transmitter at the monitoring station transmits a distinctive carrier signal over the power lines to said protected premises which is unmodulated in the absence of a response by said monitoring equipment to an intrusion alarm signal from said protected premises and which is modulated when such a response occurs;

14. An alarm system according to claim 13, wherein said selectively operable means at the protected premises may be operated to de-activate the alarm monitoring equipment at the monitoring station from responding to intrusion alarm signals at said protected premises. v

15. In an alarm system having:

intrusion alarm condition-signalling means at a protected premises;

alarm monitoring equipment for receiving alarm signals at a monitoring station which is linked to the protected premises through electrical power lines;

modulating means and for selecting the modulating frequency.

16. An alarm system according to claim 15, and further comprising means at the monitoring station for receiving the modulated carrier signal coming over the power lines from said protected premises and for responding separately to the two different modulating frequencies to condition the alarm monitoring equipment at the monitoring station to respond to alarm signals from said protected premises.

17. An alarm system according to claim 16, wherein said means for responding separately to the two different modulating frequencies is sensitive to the sequence in which said two different modulating frequencies are transmitted over the power lines from said protected premises to the monitoring station.

18. An alarm system according to claim 17, wherein said means for responding separately to the two different modulating frequencies comprises:

means coupled to the output of said second decoder for conditioning the alarm monitoring equipment at the monitoring station to respond to intrusion alarm signals from said protected premises in response to the activation of the second decoder by an incoming F2 signal;

selectively operable means at the protected premises for transmitting signals over the power lines to the monitoring station to activate the monitoring equipment there to respond to intrusion alarm signals from the protected premises; the improvement which comprises means for preventing said selectively operable means for activating the monitoring equipment at the monitoring station when an intrusion alarm condition already exists at said protected premises.

Claims

1. In an alarm system having: a monitoring station with alarm monitoring equipment; a protected premises which is interconnected with the monitoring station through electrical power lines; a radio link comprising one or more radio transmitters at the protected premises for transmitting an intrusion alarm signal when an intrusion alarm condition is detected there, and a radio receiver at the monitoring station for receiving said radio alarm signals and operatively coupled to said alarm monitoring equipment to actuate the latter when a radio alarm signal is received; and a power line link comprising means selectively operable at the protected premises for transmitting over power lines to the monitoring station signals for activating the alarm monitoring equipment there to respond to intrusion alarm signals broadcast from the protected premises; the improvement wherein said power line link further comprises means at the monitoring station for transmitting over power lines to the protected premises signal information as to whether the alarm monitoring equipment there is activated to respond to intrusion alarm signals broadcast from said protected premises.

4. An alarm system according to claim 3, and further comprising: means for modifying said last-mentioned signal when the radio receiver at the monitoring station receives an intrusion alarm signal from said protected premises.

5. An alarm system according to claim 4, wherein said transmitting means at the monitoring station transmits a distinctive carrier signal over the power lines to said protected premises which is unmodulated in the absence of an intrusion alarm signal received from said protected premises and which is modulated when such reception occurs; and said means at the protected premises for responding to said last-mentioned signal produces different indications for unmodulated and modulated signals, respectively.

6. In an alarm system having: a monitoring station with alarm monitoring equipment; a protected premises which is interconnected with the monitoring station through electrical power lines; a radio link comprising one or more radio transmitters at the protected premises for transmitting on intrusion alarm signal when an intrusion alarm condition is detected there, and a radio receiver at the monitoring station for receiving said radio alarm signals and operatively coupled to said alarm monitoring equipment to actuate the latter when a radio alarm signal is received; and a power line link comprising means selectively operable at the protected premises for transmitting over power lines to the monitoring station signals for activating the alarm monitoring equipment there to respond to intrusion alarm signals broadcast from the protected premises; the improvement wherein said selectively operable means at the protected premises comprises; means for applying a carrier signal to the power lines to be transmitted to the monitoring station; means for modulating said carrier signal at either of two different frequencies; and selectively operable means for activating said modulating means and for selecting the modulating frequency.

9. An alarm system according to claim 8, wherein said means for responding separately to the two different modulating frequencies comprises; a first decoder that is sensitive substantially only to a first modulating frequency, F1; a second decoder that is sensitive substantially only to a second modulating frequency, F2; means coupled to the output of said second decoder for conditioning the alarm monitoring equipment at the monitoring station to respond to intrusion alarm signals from said protected premises in response to the activation of the second decoder by an incoming F2 signal; and circuit means interconnecting said first and second decoders for inhibiting the second decoder from being activated by an incoming F2 signal until after said first decoder has received an F1 signal.

10. An alarm system according to claim 9, and further comprising means acting between said radio receiver at the monitoring station and said second decoder for inhibiting the latter from being activated by an incoming F2 signal when said receiver receives an intrusion alarm signal from said protected premises.

11. In an alarm system having: intrusion alarm condition-signalling means at a protected premises; alarm monitoring equipment for receiving alarm signals at a monitoring station which is linked to the protected premises through electrical power lines; and selectively operable means at the protected premises for transmitting signals over the power lines to the monitoring station to activate the monitoring equipment there to respond to intrusion alarm signals from the protected premises; the improvement which comprises: a transmitter at the monitoring station for transmitting a signal over the power lines to the protected premises when the alarm monitoring equipment at the monitoring station is conditioned to respond to intrusion alarm signals from the protected premises; and means at the protected premises for responding to said last-mentioned signal.

12. An alarm system according to claim 11, and further comprising: means for modifying said last-mentioned signal when the alarm monitoring equipment responds to an intrusion alarm signal from said protected premises.

13. An alarm system according to claim 12, wherein said transmitter at the monitoring station transmits a distinctive carrier signal over the power lines to said protected premises which is unmodulated in the absence of a response by said monitoring equipment to an intrusion alarm signal from said protected premises and which is modulated when such a response occurs; and said means at the protected premises for responding to said last-mentioned signal produces different indications for unmodulated and modulated signals, respectively.

14. An alarm system according to claim 13, wherein said selectively operable means at the protected premises may be operated to de-activate the alarm monitoring equipment at the monitoring station from responding to intrusion alarm signals at said protected premises.

15. In an alarm system having: intrusion alarm condition-signalling means at a protected premises; alarm monitoring equipment for receiving alarm signals at a monitoring station which is linked to the protected premises through electrical power lines; and selectively operable means at the protected premises for transmiTting signals over the power lines to the monitoring station to activate the monitoring equipment there to respond to intrusion alarm signals from the protected premises; the improvement wherein said selectively operable means at the protected premises comprises: means for applying a carrier signal to the power lines to be transmitted to the monitoring station; means for modulating said carrier signal at either of two different frequencies; and selectively operable means for activating said modulating means and for selecting the modulating frequency.

18. An alarm system according to claim 17, wherein said means for responding separately to the two different modulating frequencies comprises: a first decoder that is sensitive substantially only to a first modulating frequency, F1; a second decoder that is sensitive substantially only to a second modulating frequency, F2; means coupled to the output of said second decoder for conditioning the alarm monitoring equipment at the monitoring station to respond to intrusion alarm signals from said protected premises in response to the activation of the second decoder by an incoming F2 signal; and circuit means interconnecting said first and second decoders for inhibiting the second decoder from being activated by an incoming F2 signal until after said first decoder has received an F1 signal.

19. An alarm system according to claim 18, and further comprising means at the monitoring station operable in response to receipt of an intrusion alarm signal for inhibiting the second decoder from being activated by an incoming F2 signal.

20. In an alarm system having: intrusion alarm condition-signalling means at a protected premises; alarm monitoring equipment for receiving alarm signals at a monitoring station which is linked to the protected premises through electrical power lines; selectively operable means at the protected premises for transmitting signals over the power lines to the monitoring station to activate the monitoring equipment there to respond to intrusion alarm signals from the protected premises; the improvement which comprises means for preventing said selectively operable means for activating the monitoring equipment at the monitoring station when an intrusion alarm condition already exists at said protected premises.