If you are already using or plan to purchase the ElkGuard Wireless Home Security System or the ElkGuard Wireless Home Security System with Cellular GSM , the ElkGuard PIR Wireless Motion Detector is an excellent accessory. It can be added to either wireless security system to sense movement, and because each system can handle up to 23 additional devices, you can place multiple units throughout your home. This battery powered device communicates wirelessly via radio frequency (RF), so difficult in-wall wiring or hardwired connections aren't required. It will send an alarm signal when movement has been detected or if the unit is being tampered with, it will also send a signal when the battery is running low. With a broad 90 angle of detection and a sensing range of up to 48 feet, this reliable sensor can boost security on any ElkGuard system. This product requires the use of a 9-Volt Lithium Battery, included. This product is also available as a Pet Immune PIR Wireless Motion Detector or Slimline PIR Wireless Motion Detector Battery Saving Timer The ElkGuard PIR Motion Detector has a unique battery saving feature which means you must wait five minutes between activations. To test the motion detector, leave the room for at least five minutes and then re-enter. The red light in the sensor will flash to indicate that it has sensed your motion into the room. If you don't see the red light you may not have waited long enough. Adjustable Pulse Count To fine tune the settings and prevent false alarms, you can manually set the number of times (from one to four) the main unit motion detection beam needs to be crossed before an alarm occurs.