Uxcell a10103000ux0020 Recessed Security Alarm Contacts Door Window Sensor Magnetic Reed Switch White;

Switch Type: 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 ).
For example: Install on the door, close door light on. open door light off.
When make order,pls check carefully!
The reed switch is an electrical switch operated by an applied magnetic field.
Designed for use with alarm systems. Great for use in family and factory window, door. etc..
Easy to install.