Magnetic alarm connectors can be used on doors, windows and skylights. Image Credit: Comstock/Comstock/Getty Images
Magnetic alarm connectors are a vital part of many intruder prevention systems, helping to secure your home by allowing the system to monitor whether doors and windows are open or not. The contacts have an electrical circuit running through them that breaks if a door is opened, triggering an alarm or other security response. Knowing the types of magnetic contact and how they operate could help you to troubleshoot problems with your home alarm system.
Operation
Magnetic alarm contacts come in two parts: a magnet and a circuit. The magnet is attached to the door itself, while the circuit is wired to the in-house security system and lies on the door frame. The circuit has a switch that is designed to remain closed while it is subjected to magnetic forces. As such, the circuit is completed when the door is closed. If the door is opened, however, the switch returns to an open position due to there no longer being magnetic forces acting on it.
Reed Switch
The switch used in magnetic alarm contacts is known as a reed switch. Reed switches consist of two magnetic fibres, or reeds, that are sealed in a glass casing and physically move apart when the door is opened, breaking the switch's circuit. For this process to work, the switch must be correctly calibrated so that it is closed when the door is shut and opens when the door is moved to a sufficient degree.
Types
From a physical standpoint, there are two main types of alarm contacts: flush contacts and surface contacts. Flush contacts are designed to be embedded into the door and its frame during installation, making them very discreet so that intruders may not realize they are there. However, flush contacts take a lot of work to install and can only be fitted to certain materials. Surface contacts sit outside the door and so are less discreet, but they are also more versatile as they can be fitted to both doors and windows.
Uses
In general, magnetic alarm switches are used to trigger alarm systems when their circuit breaks, but they can have other security-related uses as well. For example, some systems can be configured to automatically warn security services if a door is opened rather than sounding an alarm. In addition, magnetic contacts can be used to trigger CCTV recordings. Magnetic CCTV contacts sometimes use a "normally open" configuration, where the switch is open by default and closes when the door opens.
