This Drive Way Alert system will alert you if a car or person passes by the transmitter. Simply place the transmitter near the entrance to your driveway, anything passing by the transmitter will cause the receiver to sound a pleasant chime. Can also be placed by the front door to alert you if small children (or big children at night!) try to leave the home. Will alert business owners, working in the back, to customers entering their store. Simple installation. 150 ft. recommended maximum line-of-sight wireless transmission distance between sensor and receiver (approx. 75' to 125' wireless range through 1 outside wall). Requires one 9 volt and three 'C' batteries.