A wearable transmitter assembly includes a housing containing a radio frequency transmitter and tamper detecting circuit that are attached to an appendage of an individual with a buckle and strap. A light emitter and a light sensor are disposed in the housing and extend to the outside of the housing...http://www.google.com.au/patents/US5650766?utm_source=gb-gplus-sharePatent US5650766 - Wearable transmitter with optical tamper detection
