Product Name: Magnetic Door Switch; Model: MC-33C
Contact Type: NC (Normally Closed)
Work as an anti-theft alarm, ideal for metal door and window
NC means Normally Closed:When the magnet together, the circuit is conductive( light on ); when the magnet separate, the circuit is not conductive ( light off )
These are the door contact sensors that are in use with any and all commercial or residential card access systems as well as all security burglar alarm system