Don"t be caught off-guard... Wireless Driveway Alert and Alarm System warns you that visitors are on their way to your door This driveway alert system uses a wireless receiver in your home will chime when the infrared driveway alert sensor outside detects motion, so you"ll be prepared for that unexpected knock at the door or beep in your driveway. This driveway alert"s wireless motion sensor mounts outside on a post or wall, and you can set the receiver anywhere in your house (within 200 ft. of the sensor). Completely wireless installation Weather-resistant plastic housings Mounting hardware includedRequires one 9 volt and three C batteries (sold separately).