Instantly be alerted when someone pulls into or out of your driveway. Functional range of up to 400 feet from indoor receiver to driveway sensor/transmitter. Indoor receiver chime announces the arrival of a vehicle in the driveway. Electromagnetic technology detects vehicles entering and exiting driveway, and alerts you with an indoor chime. Does not detect people, animals or wind movement. Transmitter requires 2 "AA" batteries (not included). The driveway alert contains: Mounting stake, outdoor driveway sensor and transmitter, indoor receiver and transformer.