SECURITY ALARM REED SWITCH - DOUBLE THROW

You have both types of contacts on the one unit, so you will always have the correct one! Normally Open (N.O.) and Normally Closed (N.C.) per pair. Contact operation: Contacts are closed cicuit when the magnet is alongside the switch. For alarm installation this is denoted as the "normal" state as the door/window is secure and the alarm is armed.