These PIR (Passive Infra-red) sensors will detect any movement within a defined area, alerting you of any potential intrusion before it occurs. The PIR (Passive Infra-Red) is a motion sensor that sits near the entrance or exit of your rooms and detects any movement. Another great feature is that they are also pet proof – so no need to worry about your family dog, car or rabbit setting off the alarm in the middle of the night.