XCSOURCE Wireless IR Entry Welcome Device Door Bell Chime Motion Sensor Auto Alarm HS237 Attach this infrared alarm anywhere you want and instantly know when someone crosses the beam. Infrared sensor detects motion and sends a signal to the receiver. Wireless installation, just place the sensor at the entrance. Great for retail store, shops, business, salons, front / back / side door, etc. Receiver requires 2* AA batteries, transmitter requires 1* 9V battery (batteries are not included).