Infrared signal processing for motion detectors

An apparatus and method of processing signals from a passive infrared (PIR) motion sensor evaluates energy of received signals. An integration or accumulation process can be used to provide an indicator of signal energy. This indicator can be compared to a predetermined alarm threshold to determine if an alarm indication should be generated. Evaluating circuitry (170a, Fig 3) receives sensor signals 510 and may determine if an alarm should be generated by digitally integrating the signal during a sample interval 530. Alternatively an amplitude oriented method may be used which involves forming a plurality of differential signal values. The motion detector may be used to detect an intruder in a monitored area of space. Alarm determinations are more effective in the presence of smaller sensor output signals and false alarms are eliminated to a greater extent than in previous PIR-type detectors.