Principle of door magnetic switch: The magnetic contact sensors is mainly composed of a switch part and a magnet part. Among them, the switch part is mainly a normally open dry reed tube; The magnet part is mainly a permanent magnet with a permanent magnet inside, which is used to provide a stable magnetic field. When the switch part is very close to the magnet part, that is, when the door or window is closed, the magnetic door contacts is in the working state, and the alarm sound will be sent out after receiving the attack of forced intruders; When the switch part is far away from the magnet part, that is, the door or window is open, there is no forced intrusion, and the Magnetic Sensors is closed. FBelec 20year's manufacturer in alarm magnetic sensor,if you need more information,please contact FBelec