What Are Door Contacts?

Door contacts are sensors that let a system know whether a door is opened or closed. These are some of the most common sensors used with alarm systems. They are extremely easy to use, and they can be programmed in a number of different ways. These sensors can be wireless or hardwired.

Door contact sensors consist of two (2) parts. These parts are a sensor and a magnet. If the device is surface-mounted, then the sensor and magnet will be installed on the surface of the door and its frame. If the sensor is recessed, then the sensor and magnet will be inserted into holes that are drilled into the door and its frame. Regardless of whether you use surface-mounted contacts or recessed contacts, the manner of operation is still the same. The standard practice is to have the sensor on or inside the door frame, while the magnet is on or inside the door itself. This is to prevent damage to the sensor. The magnet can take more abuse than the sensor and still work.

The idea with a door contact is to have the sensor and magnet properly aligned. When the door is closed, the sensor and magnet must usually be within one half-inch of each other. This maximum allowable magnet spacing gap can vary between different sensors, but one half-inch is usually the standard distance. Ideally, the sensor and magnet should be in direct contact when the door is closed. This is why these sensors are called "door contacts". Opening the door will cause the magnet to become separated from the sensor. This will release a metal reed switch inside the sensor. The sensor will recognize and report the change in status to the alarm control panel.

There are also mechanical door contacts called plunger switches. These one-piece recessed door contacts install in the door frame and rely on the door itself to push the plunger style switch in, thereby closing the circuit. This will indicate to the alarm panel that the door is closed. When the door is opened, the plunger switch is then allowed to decompress, opening the circuit and indicating to the alarm system that the door is open. In order to use these switches, the gap between the door and the door frame must be just the right distance. Check the installation instructions for the contact being used for the proper gap. These contacts can be installed on either the knob side or the hinge side of the door. They can also be used with sliding doors, as long as a hole for mounting can be drilled.

You can program a door contact with an alarm system in many different ways. Some of the most common Zone Types or Response Types used with door contacts include Entry/Exit, Perimeter, and Interior Follower. An Entry/Exit Zone Type will require you to disarm the system within a set Entry Delay Period if the sensor is faulted while the system is Armed Stay or Armed Away. Failure to disarm in time will result in an alarm. A Perimeter Zone Type will initiate an immediate alarm if the sensor is faulted while the system is Armed Stay or Armed Away. An Interior Follower Zone will initiate an immediate alarm if the sensor is faulted while the system is Armed Away, unless an Entry/Exit Zone is faulted first. However, Interior Follower Zones are automatically bypassed when the system is Armed Stay so that anyone inside the building can move throughout the premises freely. There are other Zone Types that are sometimes used with door contact sensors, but these are the most common.