Add an Extra Wireless Transmitter for the Wireless Motion Alert system (sold separately), and you'll be able to monitor another entrance to your property. This weatherproof transmitter operates on one 9-volt battery (sold separately) and is easily mounted on a tree or post near the driveway (mounting materials sold separately). The transmitter uses a passive infrared (PIR) beam to detect people or vehicles to a distance of up to 80 feet, then sends a radio signal back to the receiver, which can be placed in your home up to 3000 feet away. Using the dip switches on the Extra Wireless Transmitter, you can select one of four tones (Classical, Westminster Chime, Ding Dong, or Whistle) to sound when the receiver gets the signal from the transmitter. The tone will sound for a few seconds.