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 Slimline 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. The extremely compact design of this product makes it ideal for discrete placement. 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 38 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 a standard PIR Wireless Motion Detector more info