Essential Info If you need a motion detector thats virtually unnoticeable, youve found it. This compact PIR motion detector measures just 3/4" in diameter and is only 2 3/4" long. It has normally closed contacts which allows it to work with virtually any security system (for alarm purposes) or automation system (to automatically activate lights or other devices when you walk into a room). The unit has a powerful 35' detection range and a 17 field of view. Requires 12VDC power (supplied by the alarm system).