magnetic contact
A magnetic contact is a component of alarm systems such as those used in industrial and office buildings and in residential houses.
They are sensors that are placed on windows and doors and when opened, trigger a contact that can be used to activate an alarm or for other purposes when the alarm system is turned on. Such an opening sensor consists of two parts placed close to each other. One part on the window or door frame, the second on the movable frame. In one part there is a reed relay with its switching contacts, in the other there is a permanent magnet, the magnetic flux of which flows through the reed relay.
When the part with the permanent magnet is removed from the reed relay, the magnetic flow is interrupted, which changes the signal state. This change is used to trigger the alarm.