Defender AL101-TX Add-On Motion Sensor for Wireless Driveway Alert System with 300-Feet Range ADD-ON For use with the AL101 Wireless Driveway Alert System Place the motion sensor in your driveway or restricted areas to be notified when people are present Sensor is weather resistant for year-round use Wireless signal allows the motion detector to be installed up to 300ft from the alarm unit 3 total sensors can be used with the main system