Casa Security

Motion Detectors vs. Window Sensors: What’s the Difference?

People walking around

The majority of security systems today incorporate both motion detectors and window sensors as part of the overall package. These devices play an important role in securing your property and it’s crucial that you understand how they work to ensure they function properly. For homeowners who are relatively new to security systems, motion detectors and window sensors, may appear similar at first, but in reality, they function differently in terms of how they protect your home/establishment.

The question is, what exactly are motion detectors and window sensors? How do they differ from one another and what are the advantages and disadvantages of using them? This article will explain how these devices work and why you should consider investing in them.

What is a motion detector?

A motion detector (also known as a motion sensor) is a device that detects movement in a given area. There are two types of motion detectors used in security systems and these are; active motion detectors and passive motion detectors

An active motion detector emits ultrasonic sound waves that reflect back to its sensor. This reflection of sound waves continues until an interference disrupts it (e.g. a person walking past it). This sounds off the alarm and notifies the homeowner that someone has accessed their property.

A passive motion detector on the other hand, works by detecting infrared energy emitted by humans (and animals) in the form of heat. When the sensor detects a spike in infrared energy, the alarm sounds off. There is a certain heat threshold that needs to be exceed in order for the sensor to trigger the alarm, thus limiting the number of false alarms.

Pros of motion detectors:

  • Detects movement with high levels of accuracy.
  • Creates a solid security perimeter when used in conjunction with other devices.
  • Sets off the alarm almost instantly.

Cons of motion detectors:

  • Prone to accidental triggers.
  • Can be disabled by tech-savvy burglars.

What is a window sensor?

A window sensor is a small device that’s attached to a door/window to detect forced entry. Window sensors are available in wired or wireless versions, though most security systems today use the latter for convenience and ease of use. This device has two components; a reed switch and a magnet, with one component installed in the window frame and the other component installed in the window itself.

The reed switch houses a small circuit and creates a continous loop of electrical current when the magnet comes in contact with it. This means that whenever a door or window opens, the electrical current is cut off, thus deactivating the circuit and triggering the alarm. Most window sensors are battery operated and are installed with a strong adhesive backing. Since they’re wireless, thieves and burglars will have a tough time disabling them.

Pros of window sensors:

  • Easy to set up and install.
  • Portable and wireless.
  • Triggers the alarm automatically whenever a door/window opens.

Cons of window sensors:

  • Does not detect forced entry when the burglar breaks open the window.
  • Battery needs to be monitored regularly.

Choosing between motion detectors and window sensors


It’s not about choosing between motion detectors and window sensors per se, as it’s more on how to integrate them in your security system. Using these two devices together give you the best of both worlds and creates a reliable security perimeter inside your home. For example, you can use motion detectors in areas like your hallway, living room, and bedroom while you can use a window sensor on almost all areas with windows.

For the most part, you should only use motion detectors on the most important areas of your home. This is because motion detectors are very sensitive and the last thing you want is for your pet to accidentally set it off in the middle of the night. Keep in mind that when using a motion detector, avoid installing it in places where there are lots of moving objects like rustling drapes or wavy plants.

In terms of window sensors, you want to use these devices in areas where you suspect potential burglers may attempt to break in. This can be through the back windows, on the second-floor windows, and in your living room windows. Of course, relying on window sensors alone isn’t enough to deter thieves and burglars so make it a habit to double check every entry/exit point in your property and ensure all of them are locked securely.

One device we haven’t mentioned yet is a glass break sensor. Basically, it’s a device that detects the sound of glass breaking. Once it detects a shattering noise, it triggers the alarm. It’s a great device to use alongside window sensors since a window sensor alone won’t be able to detect a broken glass window by itself.