What You Need to Know about Door and Window Sensors

Door and window sensors make up the backbone of any home security system. Most systems come with a set number of sensors, and then you can add more for an additional fee. Ideally, the sensors get placed on every door and window in the home, though some people only use them on the lower level of the house to save money. If a door or window gets opened or breached when the alarm is on, the sensor sends a signal to the main control panel, triggering an alarm.

There are different types of door and window sensors, though they all perform basically the same function. Understanding how your sensors work helps you keep them well-maintained. This keeps your system performing optimally, so your risk of home invasion remains reduced.

How They Work

Door and window sensors come in two pieces. One fits onto the door or window itself, while its counterpart attaches to the frame. Adhesive usually keeps the sensors in place, though sensors can be screwed directly into the frame. Position the two pieces of the sensor right next to each other; when the two pieces are separated, such as when the door or window is opened, they send a signal to the alarm panel.


Sensors are either wired directly into your alarm system, or they have a battery to power them so they can function wirelessly. The wired sensors require more time and effort to install, while the batteries on wireless sensors need frequent checking to ensure they don’t run low. The connection between the two sensor pieces is formed in one of several ways. Some sensors rely on magnets to create the connection. When the two parts of the sensor are separated, the magnetic field is broken and the alarm goes off. Others rely on a light beam, with one piece of the sensor generating the light and the other receiving it. If the light field is breached or turned off while the system is on, the alarm activates.


Your alarm panel often alerts you when your sensors aren’t functioning properly, but conduct weekly checks anyway to discover and solve problems before they become severe. The adhesive holding the sensors in place loses strength over time. This process accelerates if your home suffers from higher humidity. If a sensor starts slipping off through a window, you are likely to experience multiple false alarm activations. Physically inspect the sensors as well as look for signs of wear. If someone accidentally hits a sensor, such as while moving furniture or something else heavy, the sensor’s function can be impeded.

Check your alarm panel regularly as well to check for error messages or warnings indicating a sensor problem. Notify your alarm company when this occurs, so they’re aware of your system problems and can help you with a solution. While sensor repair is possible, replacement is often the cheaper and safer option.

Other Types of Sensors

Door and window sensors should not be your sole line of defense in your home security system. A shatter sensor detects the sound of a window breaking, alerting your alarm system in the process. Likewise, it detects strong vibrations that a regular window sensor might not pick up on. Motion sensors often rely on infrared energy detection. As someone moves through a room, the sensor detects the changes in infrared energy and activates an alarm. It works from a distance, whereas by window sensors and only work for the door or window are attached to.

What You Need to Know about Door and Window Sensors

Count the number of doors and windows in your home when planning for a home security system. Include the garage door as well. While reducing the number of sensors you need saves money in the short term, a single unsecured or unmonitored door renders your entire security system useless. Shop around when looking for a new system or when replacing your existing sensors to make sure you get the best deal possible. Ask about any special discounts currently available. A dealer is likely to cut you a price break if you ask for one because the home security industry is so competitive and he wants your business.

Door sensors are an essential component of your home security system: they let you know when someone is entering your home. These devices are made up of two parts, which form a circuit when they’re kept parallel to each other. When someone opens the door, the two parts separate and break the circuit, which triggers the control panel to sound an alarm.

Because door sensors are simple to install, it’s easy to take these helpful gadgets for granted. But the more you know how your home security system works, the better you can use and maintain them.

The Inner Workings of a Door Sensor

While there are several different types and styles of door alarm sensors, most use a reed switch and a magnet to determine when a door is open or closed.

Reed switches are used in countless devices, from doorbells to laptops, and rely on a set of electrical connectors. The switch is closed when the two parts are sitting close to one another, and an electric current can flow. When the switch opens, the two parts separate, causing the electrical current to stop and the circuit to deactivate.

When you add a door sensor into your home security system, the device will come with both pieces: a reed switch and a magnet. One piece attaches on the door frame, and the other attaches parallel to the first piece on the door itself. The two parts create a closed circuit when the door is shut. As the door opens, the magnet and switch separate, breaking the circuit. When the circuit breaks, the sensor signals the central control panel.

Installing Door Sensors

Door sensors are easy to install. Using a strong adhesive, attach one piece of the sensor onto the door and the other to the frame.

The two pieces must sit directly next to each other with only a small amount of space between them. If they’re too far away or aren’t parallel to one another, the pieces can’t interact and the reed switch and magnet won’t create a circuit.

Garage Door Sensors

Though not as common as regular door sensors, garage door sensors can bring a lot to a home security system. There are two ways to detect a garage door opening: with a standard door sensor or with a pitch sensor.

The standard sensor works the same as on any other door. The two pieces are installed next to each other, one on the door and one on the wall right next to the door. When the garage door is raised, it breaks the circuit and sets off the alarm.

A pitch sensor is a bit different. Rather than working through two pieces, pitch sensors are standalone devices. They’re designed to detect changes in angle. When the garage door is closed, the sensor sits vertically; when the door is opened, the sensor will move up with the door, and that change in angle will set off the sensor to trigger the alarm.

Door Sensor Use and Maintenance

Depending on the security system, you may be able to customize the type of alert you receive when a door opens. You may choose for an audible alarm to sound when a door opens. Or, you may prefer the alarm to trigger silently while alerting your security company and notifying you of a possible breach.

No door sensor lasts forever. The sensor may become damaged, the switch may wear out, and wireless sensors eventually run out of batteries. If a door sensor is setting off false alarms or malfunctioning, make sure to call your home security company to replace it immediately.

Now that you know the inner workings of door alarm sensors, it’s time to shop around and find one that meets your home security needs. Check out our guide to door and window sensors for comprehensive reviews of our top picks.


Leave a Reply

Your email address will not be published. Required fields are marked *

Begin typing your search above and press return to search. Press Esc to cancel.