Reed Switch is a switch that is enclosed in a small glass tube, that is controlled by a magnet or magnetic field acting on it. It is magnetically operated switch usually mounted on doors, but may be mounted on windows, designed to detect their movement. Upon movement detection sends a signal to the control box which then sounds the siren.

Reed Switch Diagram

Reed switch is an electric switch that consists of a pair of ferrous metal contacts in a hermetically sealed glass envelope. A permanent magnet placed in close proximity to the switch will cause the contacts to pull together, thus completing an electrical circuit.