How Does a Window Sensor Work? And Other Important Questions

Window sensors seem a little mystical, but it’s just cool science

Brianne Sandorf
Sep 06, 2022
Icon Time To Read2 min read

Sensors that know when your windows are open or closed? It kinda sounds too good to be true—but it’s not!

We’ll explain why you might want a window sensor, how it works, which one is best for you, and how to install it.

Why use a window sensor?

Window sensors are one of the most basic but effective ways to secure your home. Intruders favor windows because they’re an easy route into a house.

Protecting your windows makes it crazy difficult for an intruder to get in.

Some window sensors can also be connected to many other devices in your smart home hub.

How does a window sensor work?

The quick-and-dirty answer is magnets.

The more complicated answer is that the sensor comes in two pieces, one for each side of the window frame. One side contains a magnet. The other contains a little thingummy called a reed switch. Like Romeo and Juliet, the magnet and the reed switch long to be together. As long as they’re close enough to sense each other, all is well.

But when the window opens, the two halves are torn asunder. The loss of magnetic connection flips the reed switch, which causes the alarm to go off.

Ta-da! Now you know there’s an intruder in your home.

(To help you get the idea, we’ve included a photo of a Vivint door sensor that works on a similar principle.)

Copy of vivint-door-sensor
What if the intruder breaks the window?
Info Box

If you’re worried about broken windows, you’ll also want a glass break sensor. This handy-dandy smart device listens for the tinkling sound of breaking glass.

Which window sensor should I choose?

Window sensors come in a lot of options.

First, you have to decide if you want wired sensors or wireless. While some sensors are hardwired into the home electrical system, most security manufacturers offer wireless sensors only. If you want wired sensors, it’ll take a little more work to find them. (Or not, since we found some for you.)

Your second choice: should you buy standalone sensors or sensors that are part of a bigger home security system? We typically recommend the full home security system approach because there’s more built-in protection. A full home security system typically includes the sensors, motion detectors, a hub or control panel, and maybe some security cameras.

Top home security systems with sensors
Provider
Window sensor image
Window sensor price
Installation type
Details
Vivint
Vivint_sensor
$50.00Professional
SimpliSafe
simplisafe sensor
$14.99DIY
Frontpoint
Frontpoint sensor
$24.74DIY
ADT
ADT_sensor
Check with providerProfessional
Brinks Home
Brinks Home _sensor
$29.00DIY, professional

Data effective 08/01/2022. Offers subject to change.

Door/window sensors and more
Heads Up

A lot of home security companies sell combined door/window sensors—you pick where you want to use them. And some companies, like Ring Alarm, call their door or window sensors “contact sensors” or “entry sensors.”

If you want sensors only, you can try a standalone kit like this one from Fuers.

How do you install a window sensor?

Some window sensors require professional installation, but some you can install yourself.

Sensors should work equally well on windows that slide and windows that swing open. Just note that the two sensor halves usually need to be on the same plane to work.

If one half is on a taller surface than the other, the magnet may not meet the reed switch. In that case, you might want to look for a recessed sensor that goes inside the window frame.

Self-installed sensors generally come with a gentle adhesive or Velcro base so you can easily remove them.

When installing a DIY wireless window sensor, the steps will almost always look something like this:

  1. Choose the installation site.
  2. Wipe the site down with a disinfectant or cleaner.
  3. Activate the sensor and connect it to the alarm.
  4. Prepare the adhesive.
  5. Install the two sensor halves by pressing the adhesive sides to the installation site.

Recap

Now that we’ve answered all your questions about window sensors, let’s review what we’ve learned super quickly.

  • Why use a window sensor? It’ll keep your home safer.
  • How does a window sensor work? Magnets, mostly.
  • Which window sensor should I choose? That depends on whether you want wired or wireless and a complete security system or a standalone setup.
  • How do you install a window sensor? You might have to do it yourself, but it’s usually pretty straightforward.

Now that you know about window sensors, learn about motion sensors.

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Learn about motion sensors

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Learn about motion sensor lights

Brianne Sandorf
Written by
After five years with Reviews.org, Brianne can and will tell you which internet or mobile provider you should sign up for. She’s talked with internet customers across the U.S. and beyond and addresses their real-life concerns in every piece she writes. Brianne also created the ratings system for the Reviews.org internet service provider reviews and wrote most of them. Brianne channels her lifelong interest in detective work by hunting for obscure, need-to-know information about internet service providers. She’s always learning so that she can pass her knowledge on to Reviews.org readers. Her writing and expertise have appeared in numerous other publications, including Move.org, Parents.com, and the Stanford student blog. Her work for Reviews.org is also cited in a research paper about smart home assistants titled “Expert-Generated Privacy Q&A Dataset for Conversational AI and User Study Insights.” Brianne is a homegrown Utahn who loves to travel and see new places. She graduated from Westminster College with a double major in honors and creative writing. After 20 years in a 8,000-person city, she now lives in Murray, a bustling metropolis of 50,000 where she and her husband raise their two little girls.

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