What is a Door Contact Sensor?

A contact sensor is an important component of security systems and smart homes. Although it was originally designed to detect when intruders open windows or doors, the device has evolved over the years to offer more functions. It provides the data smart homes need to take intelligent actions.

A contact sensor can turn your lights on, trigger smart door alarm on your smartphone or control a smart thermostat, among other functions.

How Does It Work?

Door contact sensors tell a security system if doors are closed or open. They can be installed all over a house on the windows, doors or even desk drawers. Available in two pieces, one part of contact sensors is installed on the door while the other piece is fixed on the door jamb or frame.

During installation, the two pieces of contact sensors are placed next to each other. Built to use magnetic fields, the two pieces track door movements. They drift apart if the door is open, causing the contact sensor to transmit ‘open’ signals to the security system. Here’s a YouTube video detailing how door contact sensors work.

Various Types of Door Contact Sensors

Door contact sensors can either be wired or wireless. The following are various types of wired and wireless contact sensors for doors and windows:

Overhead Door Contact Sensors

Featuring armored cables linked to the switch to withstand more wear, overhead door contacts are used on large roll up garage doors. Garage doors don’t have close tolerance when closed, hence the need for wide gap contact sensors. Otherwise, they are prone to false alarms.

‍Overhead Contact Sensors
‍Overhead Contact Sensors

Roller Ball Door Contact Sensors

Installed on door jams on the hinge side, roller ball door contacts are recessed. However, they feature ball protrusions after installation. The contact closes when doors are closed and opens when the converse is true, triggering the alarm.

Roller Ball Contact Sensor
‍‍Roller Ball Contact Sensor

Surface-Mount Door Contact Sensors

Wired connections are used to link the contact to the control panel. Although it can be used as a wireless contact sensor, surface-mount door contacts are increasingly becoming outdated with increased popularity of wireless home security systems.

Contact Sensor
Surface mount door contact sensors

Pull Apart Contact Sensors

Built with a hole and a magnet, the latter slides into the former to complete the circuit; if a door is opened, and the system is armed, the contact opens and triggers the alarm. Pull apart contact sensors are often used on gates.

Pull Apart Contact Sensor
‍Pull Apart Contact Sensor

Recessed Door Contact Sensors

These contact sensors are installed inside windows or doors. Connections are soldered so the wire can move easily into the hole to make contact. Recessed wireless contact sensors are used with wireless home security or alarm systems.

Recessed Contact Sensor
‍Recessed Contact Sensor

Why is it Important to Have Door Contact Sensors?

Contact sensors come in two parts that make contact when a condition is met, for instance, if a door or window opens. According to an article published on the New York Times, home security systems are important in deterring crime, among other benefits. The following are the top functions of door contact sensors, hence the importance of having them installed in home security systems:

1. Activates/Triggers Alarms

Traditionally, contact sensors were used in security systems to trigger alarms if an intrusion is detected. If contact sensors transmit ‘open’ window or door signals in an armed security system, the alarm is triggered. Otherwise the converse is true.

2. Generates Real-Time Smartphone Alerts

Contact sensors can also generate real-time alerts on your martphone, each time ‘open’ or ‘closed’ signals are transmitted. With the information, homeowners can know when doors in their houses are opened. Depending on the type of information a homeowner needs, alerts can be customized to provide specific important information.

For instance, the contact sensors can be configured to trigger real-time alerts if homeowners leave their houses without closing doors. Similarly, going to bed with some windows open can also cause contact sensors to trigger alerts on Smartphone devices.

3. Offers Protection

Due to ease-of-installation and the wireless nature of contact sensors, homeowners can use them to keep track of different things as follows:

Valuables – Contact sensors can help keep track of valuables such as jewelry boxes and safes, letting owners know when they are accessed or left open.

Yard – Usable in yards, homeowners can receive alerts whenever the pool area is accessed or the gate is opened from the street or yard.

Food – If food is prone to defrosting due to an open freezer drawer, door contact sensors can transmit signals to homeowners to take action.

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4. Activates/Triggers Devices in the Same Security or Smart Home System

In addition to activating and transmitting alerts, contact sensors can automatically trigger or activate various devices on the same security or smart home system. The sensors feed real-time data into the system to activate other connected devices. For instance, take a look at the following:

Smart Lighting – If a yard gate is swung open at night, contact sensors can be configured to turn on porch lights.

Setback of Thermostats – Contact sensors can trigger automatic thermostat set back if they detect open windows or doors. The move can help save energy for as long as the door remains open.

Door contact sensors can also be used as door bells and to offer protection for outdoor equipment such as ductless mini split air conditioners.


With benefits ranging from increased home security to better protection of valuables, homes can benefit a great deal from door contact sensors. What’s important is having the right type of door contact installed on the type of door or windows it is meant for. It’s also important for the alarm system to be armed for contact sensors to work. Furthermore, the sensors can be installed on doors or windows or any other important part of the home in need of tracking.

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