Add an Extra Wireless Transmitter for the Wireless Probe Driveway Alert system (sold separately), and you'll be able to monitor another entrance to your property. This transmitter will send an instant alert from the foot of your driveway when a car enters your property but won't be triggered by deer or large animals. A probe is buried at the base of your driveway and sends a signal to the transmitter when a car is detected. The 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 sends a radio signal back to the receiver, which can be placed in your home up to 600 feet away. The Extra Transmitter for Wireless Probe Driveway Alert comes with 50 feet of direct burial wire connecting the probe to the exterior case. The probe is buried parallel to the driveway, and will detect vehicles passing by within approximately 10 to 12 feet. The direct burial cable can be run to a tree or post nearby, where the transmitter box is located. When a vehicle drives by, the transmitter will send a signal to the receiver up to 600 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.