What Is a Security Door Sensor

A security door sensor is a contact sensor that lets a security system know when a door has been opened. These are extremely simple and easy to use devices that you will find on almost any alarm system. There are many varieties, and you can usually find one that meets your needs perfectly.

A door contact consists of two (2) parts. The larger part is called the sensor, and the smaller part is called the magnet. The sensor has a metal reed switch inside. When the sensor is next to its magnet, its internal reed switch is closed. But if the magnet becomes separated from the sensor, the reed switch is released and the circuit opens.

This is put into practice by mounting the sensor and magnet on the door and the frame. For best practice, the sensor is installed on the door frame, while the magnet is installed on the moving portion of the door. The sensor and magnet must be very close together when the door is closed for the device to work properly, usually within 0.5 inch. Gap ratings will vary per sensor model.

When the door is opened, the magnet will move away from the sensor, and the sensor's reed switch will be released. Once this happens, the sensor will send an alert to the panel so that the system knows about the opened door. A sensor can communicate with a system either wirelessly or through a hardwired connection.

When selecting a door sensor, you need to make sure it is compatible with your system. If you are hoping to add a wireless door sensor, then you must make sure you choose the wireless frequency that is supported by your system's wireless receiver. If you have a wired panel without a wireless receiver, you must add one.

Likewise, if you are hoping to add a hardwired door sensor, then you must make sure your system can support a new hardwired sensor. If you have a wired system, you will connect the new sensor to an open on-board zone or to a hardwired expansion module. Many wireless panels also have one or two zone inputs for adding wired contact sensors. Or you can add a wired to wireless converter to your wireless system so that it can support a greater number of hardwired sensors. Hardwired sensors are usually universally compatible with all hardwired alarm systems, regardless of manufacturer. The exception to this is specialty sensors, such as the V-Plex devices manufactured by Resideo (formerly Honeywell). These sensors are only compatible with the VISTA panels that support a polling loop, such as the VISTA-128BPT and VISTA-250BPT.