The Wired Driveway Vehicle Sensor allows a vehicle to drive past the sensor's 12 ft. electromagnetic field that will open your gate automatically, allowing guests the ability to exit without a Remote (FM135). This sensor detects vehicles such as cars, trucks, ATV's and motorcycles as they cross through the 12 ft. electromagnetic field. The FM138-75 is compatible with all Mighty Mule Driveway Gate Openers and Mighty Mule Slide Gate Openers.