For most security systems the door and window contacts are the first point of interaction with the outside world. Door and window contacts are made up of two pieces. They work by having one piece attached to the frame of the door or window and the other half attached to the actual door or window. When the door or window is closed the contacts are in contact. When the alarm is set and the contacts are separated the alarm goes off.

For maximum effectiveness Door and Window contacts should be placed on every outside door or window.