Product Description The 50 ft. wired Driveway Vehicle Sensor (FM138) allows a vehicle to drive past the sensor's 12 ft. magnetic field and will open your gate automatically, allowing guests the ability to exit without a Remote (FM135). From the Manufacturer Direct burial Gate Opening Sensor (also referred to as a Probe or Wand). Wires directly to the Gate Opener Control Box and senses mass metal in motion.This unit is recommended for use on the inside of the property for hands free exit by vehicles.It comes with a 50-Foot cable that should be trenched and placed next to your drive and buried no more than 12-Inches deep and no closer than 30-Feet from the gate. It will detect vehicles (cars, trucks, ATV's, motorcycles, etc.) as they cross over the 12-Foot magnetic field from the sensor and automatically open the gate as you exit.