Loop Detectors are a accessory used on Residential Gate motors, Industrial Gate motors, Building Complexes as well as Boom gate Barriers. A Loop detector or better known as a underground loop or free exit loop is a rectangular block and is made out of three or more coils made out of a conductive material like insulated copper.

The loop detector creates a magnetic field using Flux or inductance around the loop block and when it gets disturbed via metal object like a motor vehicle driving over the loop. The Loop detector then senses the disturbance and activates a signal switch. The signal switch can be used for a number of applications or functions. The trigger switch in the loop detector is usually just a simple relay with a common, normally open and normally closed contact switch. 

Where Are loop detectors used and where?  

Loop detectors in gate motors is used as a traffic control device. The Exit loop allows the gate to automatically open when guests or residents are leaving the property. Loop detectors on Barrier Gates like Traffic Booms has two functions. The first function is that the loop detector acts like a safety beam and preventing the traffic barrier from closing onto a vehicle. The second function is to open the traffic barrier for leaving guests and Residents   Read more Here.