Door Switches | Physical Devices of Home alarm systems

Door Switches :

Door switches work on a basic principle of a two-part magnetic switch. 

A switch that is sensitive to a magnetic field is mounted on the fixed structure
(frame), and wires from the switch are routed through the wall to the control panel. 

A magnet is mounted on the door in a position where it is in close
proximity to the switch when the door is closed; this also keeps the switch
closed. 

Opening the door moves the magnet away from the switch and causes 

the switch to “open,” which is sensed by the central control panel and activates an alarm. 

Magnetic switches are available as normally open (NO) or normally closed (NC) to accommodate different wiring designs and controller options.