This a magnetic switch. If no magnetic field is present, the signal line of the sensor is high (3.5 v). If a magnetic field is presented to the sensor, the signal line goes low, at the same time the led on the sensor lights up. The polarity of the magnetic field is of influence to the switching action. The front side of the sensor needs the opposite polarity as the back of the sensor to switch on.Features 100% brand new and high quality. 1. Non-contact switch 2. Hall switch integrated circuit using hall effect principle. 3. Uses the semiconductor integrated technology manufacturing magnetic susceptibility of the circuit. 4. It is by the voltage regulator, hall voltage generator, differential amplifier, schmidt triggers, temperature compensation, and the open collector output stage circuit composed of magnetic sensitive sensor circuit. 5. Its input for the magnetic induction intensity, the output is a digital voltage signal.