How Do Glass Break Sensors Work & Are They Effective?

Posted by , , at 6:03 am

In our previous two installments of Home Security 101, we covered wireless door and window sensors and wireless motion sensors. Now let’s address the third line of defense in a standard intrusion alarm system: the glass break sensor, sometimes called a broken window alarm. This device is triggered when a pane of glass shatters nearby it.

I will explain how glass break sensors work and perhaps more importantly, how effective they are. Then you can make an informed decision about whether your home would benefit from this sensor.

How Does a Glass Break Sensor Work?

There are two types of glass break sensors: acoustic and shock. They work differently, but have the same goal: to set off your home alarm when triggered.

Acoustic glass break sensors work by “hearing” the sound of breaking windows. Shock sensors work by “feeling” a physical disruption of broken glass.

Acoustic Glass Break Sensors

When a pane of glass shatters, it creates a distinct sound frequency. A glass break sensor works by “hearing” the sound of shattering glass, then triggering an alarm. That means one sensor can cover lots of windows (and glass doors) in a single room.

Shock Glass Break Sensors

Shock sensor devices work by “feeling” the unique vibrations of shattering glass. To work properly, they must be physically attached to the window or door they are protecting.

Although shock sensors are known for triggering fewer false alarms than acoustic sensors, they have significant drawbacks. For example, you need to mount a sensor on each window you wish to monitor. This can get expensive—not to mention annoying to set up.

Personally I prefer acoustic, but of course, the best glass break sensor is the one that works best for you. Effective home security is all about matching the right sensor to your lifestyle, home layout, and preferences.

Do Glass Break Sensors Really Work?

You might say to me, “Peter, this sounds all well and good, but are glass break sensors effective? And if door and window sensors and motion sensors work so well, why do I need a glass break sensor?”

The truth is, you might—or you might not.

Door and window sensors and motion sensors are fundamental parts of a home security system. I absolutely recommend those to everyone, regardless of home layout or size. However, you don’t want to have just one or two lines of defense protecting your home and family.

For instance, say a home relies solely on door and window sensors. If an intruder enters that home by breaking a window or a glass door, the door and window sensors will prove inadequate. Why? Because the window or door frame itself will remain in place, even after the pane is broken, the door and window sensors will not be triggered. The intruder will remain undetected.

Now let’s say that home also has motion sensors. This is an improvement, but the intruder can still try to avoid venturing near the motion sensor and remain undetected.

This time, however, let’s say the home also has the third line of defense that is glass break sensors. The intruder would have been detected the moment they broke the glass window or door, before even entering the home.

A glass break sensor is an extra layer of defense to make your home even safer. While it is not what I’d call mandatory, a glass break sensor absolutely helps to create a more secure home. What one sensor cannot detect, another can—and they start tag teaming to keep you and your family safe.

Glass Break Sensor Sensitivity

False alarms may occur if someone accidentally drops, say, a glass vase within the sensor’s proximity. (Often, a glass break sensor’s range is 20 feet in any direction.) There are a few other sounds that have been known to trigger acoustic glass break sensors, such as:

  • Cupboard door slam
  • A drum set’s snare drum
  • High-pitched dog barks
  • Some large captive birds, like cockatoos

You may be able to combat false alarms by testing the sensitivity of your sensor, so you know what sets it off.

Where to Place Glass Break Sensors

I’m going to take the liberty of assuming that I have convinced you to opt for acoustic glass break sensors. Now let’s set them up.

  1. Step One: For effective glass break sensor placement, you need to think like a burglar. So consider which windows are most easily accessible from the outside. Which window would you use if you were breaking into your house? Usually the answer includes any windows or glass doors on the ground floor or at the basement level. Those are the panes you most want to protect.
  2. Step Two: Decide how to distribute your sensors. You want to use as few sensors as possible to cover as many windows as possible. Areas with multiple windows are a natural starting point. For example, if you have a room with several windows and a sliding glass door, you can likely protect the whole room with a single glass break sensor.
  3. Step Three: Mount your sensors. Wireless glass break sensors mount on the wall or ceiling, and don’t have to “point” at the glass they are protecting—they just need a clear “line of sight” to do their thing.

There are a few basic rules for proper glass break sensor placement. For example, you must mount the sensor at least 4 feet away from any of the glass panes you wish to protect. It should be on a different wall from the pane. Also, never place a glass break sensor in between two windows on the same wall. There are several other factors, but if you are using a Frontpoint system, our Setup Wizard will guide you through every step of the easy peel-and-stick mounting process.

Until Next Time

The best alarm companies are committed to providing you with the protection and peace of mind you deserve. Adding one or more wireless glass break sensors to your system could be the right call for your home.

Now we’re another step closer to designing a complete home security system. There are a few more sensors to cover before we get there, so make sure to join us here for the next round.

Comments (28)

Post a Comment | View Comments
  1. Karen

    We have huge thick glass windows – commercial application – some are shatterproof (some sort of safety film on them so they will crack all to pieces but not break) and some are not. Would a glass break sensor work for us??

    • Katie Rynex

      Karen, thanks so much for reaching out! A Glass Break Sensor would not function properly on shatterproof windows, however, would work properly for the glass panel windows that will break. We hope this answers your question and ask that you please let us know if you have any other questions going forward!

  2. william

    Can the glass break sensor also be used as a listening device for conversations?

    • Katie Rynex

      William, the glass break sensors is not built for recording sounds as it can only be triggered by sounds that are in a certain frequency range. Thank you for the great question and we hope this was helpful!

  3. Maddie

    We were planning on applying security film to our rear door that has a large glass opening as an added precaution. Will the application of security film affect the GB sensor’s ability to detect that the glass has broken?

    • Katie Rynex

      Maddie, our glass break sensors detect the high frequencies emitted by broken glass. Adding the film could potentially change this frequency causing the glass break sensor to not “hear” the sound. Please let us know if you have any other questions!

  4. Mery

    I have a bird that squaks very loud and it does echo is that going to set off my glass break alarm

  5. Joan

    I recently ordered a glass break sensor for my laundry room which has a large window. I have already installed a sensor on this window. The furnace and central air conditioning are in the laundry room behind louvered doors. The room is less than 100 square feet. Will this work for me?

    • Katie Rynex

      Joan, the Glass Break Sensor should work in your laundry room, however, we recommend that you do not have that sensor armed while you are doing laundry as it may trigger an alarm. We hope this answers your question and ask that you please let us know if you have any other questions!

  6. Joan

    I recently ordered a glass break detector for my laundry room which has a large window. I have already installed a window sensor. There is also the furnace and air conditioning unit in the laundry room inside a louvered door. The room is less than 100 square feet. Will this work for me?

  7. heather

    I have GB protectors and they have gone off twice when not home and no glass broken. I assume it’s my dog barking, but she has a big low bark and barks while we are here… we have had her bark to see if it would go off. Never does. What to do now? They call and I say its proably her. They re-acitvate it at that time. Why have it then Also, it must be awful for her and my cat while it’s going of too! Suggestions?

    • Valerie Saponara

      Heather, I’ve heard of this exact situation before and it is most likely your dog. The difference here is that when you’re at home, generally dogs bark or growl but rarely whine. We have found that it is very difficult for dogs to set this alarm off, however, they are capable of whining at a certain pitch and hitting that frequency. If your dog whines even once or twice within a certain distance of that sensor when you’re not home, that could be what is setting that sensor off. I would suggest keeping your dog in another part of the home that is about 40 ft away from that sensor. I don’t have tips on how to get a dog to stop whining or whimpering, but if you think this is something that can’t be fixed, please give our Support Team a call to let them know and we can see if switching out that sensor for another is an option for you!

  8. Angela

    I have a large window in my laundry room…would the washing machine set off the glass break sensor? Also…I noticed it says not to install in small rooms, what is the reason for this?

    • Valerie Saponara

      Angela, that glass break sensor is always listening for a very specific frequency that paneled glass breaking can make. That being said, no your washing machine cannot set this sensor off. We urge our customers to put that glass break sensor in open rooms because we want to avoid echos and noises sounding louder than they are. Let me know if you have any further questions!

  9. Cynthia

    We are having trouble with our motion sensor in our den – we believe it might be getting set off by the mailman walking by our large bay window. We are considering a glass break sensor instead, but are concerned about loud noises setting it off, such as music or our smoke alarm (which tends to go off when we broil things). Is this something we need to be worried about?

    • Valerie Saponara

      Cynthia, great question. No you should not be concerned about loud noises setting that glass-break sensor off because it will only go off if it detects the sound of paneled glass breaking. You could technically drop a ceramic mug on the floor and this sensor would still not go off. It can only detect specific frequencies so you don’t have to worry about loud music or your smoke alarm sounding. Hope this helps answer your question!

  10. Toniann

    Is it possible to test a glass break sensor without breaking a window?

    • Valerie Saponara

      Toniann, yes it is! Just clap your hands a couple times in front of your glass break sensor, and you should see a little red light flash every time you clap. This means the sensor can hear you and is working properly. Let me know if you have any other questions.

      • dre

        I have a glass break sensor for my basement. Testing the sensor involves clapping your hands in front of it and if the red light goes on it works. That test did not seem very reliable to me, so while on the phone with customer service during set up, I asked to test sensor on a real window break. We have replaced half of our windows and still have the old ones. I broke 8 panes of glass, moved the control panel and the sensor to every position the tech could come up with and yet the alarm never went off. A new sensor was sent and I tried that one as well while on the phone and still the alarm never went off. Frontpoint is giving a lot of people a false sense of security with the hand clapping test. They further explained that the GE equipment sensors are tested with a GE glass break simulator and they work in that scenario. Why does my alarm not respond to actual glass from a real window? Both techs basically said to give up and use motion sensors instead. Do they know something I should know?

        • Katie Rynex

          Dre, thank you for bringing your concerns to our attention. As our equipment is manufactured by GE, we definitely stand behind its functionality and ability to alert when needed. We definitely would like to make sure that we can have all of your equipment working in optimum efficiency so we will have one of our Support Supervisors reach out to you so that they may assist. Thank you again for sharing your experience and we look forward to speaking with you soon.

  11. Kate

    About a week ago I installed glass break sensors in my home. Last night, the one in my bedroom beeped 3 times in a row. This 3 beep sequence went off about 3 times during the night. The alarm was not triggered and no glass was broken. There were raccoons going through my trash last night, but if they broke glass, why would the system just beep 3 times and not trigger the alarm? It sounded as if the beeping was coming directly from the sensor and not the control panel, but I was sleeping so I’m not entirely sure about this.

    • Valerie Saponara

      Kate, thank you for letting us know about the beeping you’re hearing. We see that you’ve recently been contacted by one of our Support Specialists regarding these beeps and they are ready to take a look into your system and find out what is going on there. Please take a look at that email and/or voice-mail when you have a second!

  12. Monica

    I recently installed window break sensor and always wondered if they worked. Unknowingly, I tested them out one day when I was putting glass dishes away in my kitchen. The loud clinking of the dishes set off the alarm. The sensor works… just don’t put away dishes when your house is armed!

  13. Monica

    I recently installed window break sensor and always wondered if they worked. Unknowingly, I tested them out one day when I was putting glass dishes away in my kitchen. The loud clinking of the dishes set off the alarm. The sensor works… just don’t put away dishes when your house is armed!

  14. Chuck Renner

    When you say the glass break listens for a specific acoustical frequency, are you saying it
    is not a ‘frequency range’?

    • Peter M. Rogers

      Chuck – Great question. The sensor actually looks for a specific frequency, but there are several it looks for – as opposed to a range. What makes the sensor so reliable is that it also uses amplitude, duration and the several individual frequencies in a combination before triggering an alarm. Thanks again.

  15. Chuck Renner

    When you say the glass break listens for a specific acoustical frequency, are you saying it
    is not a ‘frequency range’?

    • Peter M. Rogers

      Chuck – Great question. The sensor actually looks for a specific frequency, but there are several it looks for – as opposed to a range. What makes the sensor so reliable is that it also uses amplitude, duration and the several individual frequencies in a combination before triggering an alarm. Thanks again.