Product Name : PS-1301 Normally Close Cabinet Door Sensor
A proximity sensor consists of two parts: a magnetic part which contains a permanent magnet inside; and a sensor part which contains a reed switch. When these two magnetic parts get close enough, by electromagnetic induction,it will connect the electrical circuit. And this distance is called "detection distance." Usually, one of these two parts is installed on a stable position, and the other one is installed on a moveable object to connect or disconnect the circuit.