Features:Magnets are usually close to each other, which is normal statement.Close = short circuit = create a for the current.The magnets are close together and the switch is off.And the switch and magnet are separated, and the switch is open.No external power supply is needed, and the GND and N.C ports of wired or alarm control panel are directly connected.Not suitable for iron doors, it will reduce the magnetism of the sensor.Specifications:Working Distance: 15mm + 5mmSwitching Pressure: 100VDCLoad current: 300 mALife: 1 million timesSwitch Output: NC (Normally Closed)Package Weight: 91g/3.2ozPackage List:10 Pair * Door Window Sensor