Simply brilliant! Just drill a recess in your door or window and the magnet flush mounts to be invisible. The reed switch segment is similarly mounted into the door frame or window frame & wired into your system. Available in two versions to suit timber or metal frames with both versions normally closed contact.
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.