This wireless driveway alarm is the perfect driveway sensor for monitoring two entrances! This dual kit comes with two driveway sensor transmitters, two wireless receiver chimes, and two low-voltage "Original" Bells™. This Milton driveway signal bell kit and driveway alert system monitors traffic using two transmitters. The transmitters operate off of a 9-volt transistor battery. The receiver chimes plug into an ordinary electrical outlet and feature built-in volume control, and the "Original" Bells™ connect to the wireless chime and get their power from the chime. Each of the transmitters can be set to play a specific notification/tune. This means that each of the driveways being monitored can have a different sound!