Magnetic contact

A magnetic contact is a two part detector, a magnet and a contact, with one part fitted to the frame and the other to the leaf of a door or a window. When the leaf opens and the parts separate, the contact changes state and the alarm registers it.

It is the most widespread type of opening detector because it is simple and gives few false alarms if it is fitted properly. It can be wired or wireless, with a battery.

For it to work, the two parts have to be aligned and close together when the door is shut. If the door has dropped or the aluminium window closes with play, the sensor can give false alerts or fail to give them at all. Sometimes what is at fault is not the sensor but the door.

If your door rubs or does not close properly, our security upgrades page explains how we check it.