This UHPPOTE Wired Shutter Roller Magnetic Overhead Door Contact is a great choice for any access control or burglar alarm system. It is a normally closed type switch, meaning when the magnet is together, the circuit is conductive and the light is on. When the magnet is separated, the circuit is not conductive and the light is off. This contact is perfect for use in family and factory windows, doors, etc. It is easy to install and use, making it a great choice for any security system.