Single Unit. A wire free PIR motion detector for use with the Yale Easy Fit range of alarms, it activates the alarm when it detects movement however should not do so for a single animal under 27Kg.. Ideally placed in the corner of any room. When the alarm is set, the infrared sensor will pick up movement and activate the siren. Will not be triggered by a pet that weighs below 27kg (not suitable for multiple pets). For use on extra rooms that need protection, such as lounge, bedroom or extension