Intrusion detection system having improved immunity to false alarm

摘要

A multi-sensor intrusion detection system having improved immunity to false alarm has one sensor which is less susceptible to the generation of false alarm and has its output signal (20) processed and held. The held signal (42) is supplied to a logic circuit (46,48) which receives directly the signal (18) from the other sensor. The output of the logic circuit (46,48) generates an alarm signal. The sensor less susceptible to false alarm may be a microphone (12) and a circuit (22, Fig. 1A) which detects low pressure variation, and the other sensor may consist of the same microphone (12) and a circuit that produces its output signal (18) in response to audio frequency output from the microphone (12).