Personal aid signalling system

摘要

A system for use especially by the infirm or elderly for summoning the help of others who are located a distance away. The system includes a radio-type transmitter adapted to be carried in a pocket of the elderly person, and a receiver/decoder and signalling device located at an adjoining area from which signals for help or assistance can be readily observed. The transmitter unit can be activated by means of a switch or button, and emits short bursts of a modulated signal having a unique, preselected frequency. The signal is picked up by the receiver and demodulated by a detector. The decoder comprises a sensing circuit, including a gated, resettable counter which measures the frequency of the detected signal. Means connected with the counter output trigger an alarm when the transmitted frequency having the proper modulating signal is received. By the above arrangement a plurality of similar units can be disposed in the same area and operated with slightly different modulating frequencies without causing interference or interaction between them.