An alarm system that, while armed, is designed to detect and report (1) the presence of one or more unauthorized persons on the protected premises, or (2) an illegal attempt made to enter or to move within the protected premises at one or more points equipped with a sensor.
(n.) A system designed to detect and report conditions which may indicate intrusion or attempted intrusion. Source: Lock Industry Standards and Training (LIST) Council
Burglar (or intrusion), fire and safety alarms are found in electronic form today. Sensors are connected to a control unit via either a low-voltage hardwire or narrowband RF signal, which in turn connects to a means for announcing the alarm, hopefully to elicit some response. The most common security sensors indicate the opening of a door or window or detect motion via passive infrared (PIR).