The Illusion of Audio Glass Break Detection

Audio glass break detectors were intended to replace foil and save the time-consuming work needed to install and maintain this methodology.

The Illusion of Audio Glass Break Detection

Adobe Stock image by releon8211

Homes are commonly surrounded by fixed and sliding glass doors and windows. Against the foregoing backdrop, from a security system perspective, the alarm industry has always needed to pay attention to these vulnerable perimeter entry points into the home.

For those of you who have been in the industry for decades, foil was the standard of care for perimeter glass break detection.

Invariably, audio glass break detectors were in material part intended to replace foil and save all of the time-consuming work needed to install and maintain this methodology.

Given that, alarm contractors have enjoyed and continue to enjoy the benefits of being able to install one audio glass break detector to cover multiple windows as long as they were in the same room and/or in proximity to where the audio glass break sensor was ultimately placed and installed.

From first-generation single-technology audio glass break detectors to dual-technology detectors designed to detect a combination of ultra-low-frequency sounds and ultra-high-frequency sounds within a certain timeframe before an alarm condition would be initiated to help minimize false alarms, tens of millions of audio glass break detectors have been installed in homes and businesses across the country.

Fast forward to today, while audio glass break detectors have not lost their popularity, I have inspected thousands and thousands of alarm systems across the country since 1980 and have noticed a serious trend whereby audio glass break detectors are more often than not found to have been improperly installed.

In other words, despite the subscriber being able to successfully arm their alarm system, the effectiveness, and reliability of the population of audio glass break detectors in the premises equates to an intrusion detection device that may not be reliable enough to perform its intended detection function.

By way of example, either the audio glass break detector(s) are mounted too far away from the glass and/or they are found to be facing in the opposite direction of the glass that was intended to be electronically protected by the alarm system.

On the other end of the technical spectrum, to the extent that the audio glass break detectors are correctly placed and installed, the customer is found to have installed curtains and/or shades covering the entirety of the glass, and/or the subscriber has installed multiple window treatments covering their glass windows.

Resultantly, the sounds generated by forcible glass breakage into the home cannot penetrate the window treatment(s) in order to reach/travel to the microphone of the audio glass break detector and trigger the alarm system.

In other words, the sounds of breaking glass are being absorbed by/into the window coverings instead of being able to reach/travel to the microphone of the audio glass break detector. Accordingly, this intrusion detection device is unable to detect the burglarized event, and the alarm system fails. In sum, this foreseeably creates both liability and risk.

Inside the Audio Glass Break Detection Conundrum

Against the preceding backdrop, I have forensically investigated a multitude of undetected burglaries that were based upon the failure of the alarm contractor to professionally design, place, install and test audio glass break detectors in the premises and the alarm fails whereby the perpetrators are successful in their burglarious act.

Of course, the placement of window treatments can always be installed after the alarm system installation, or they are already in place when the alarm system is installed, but the installer does not recognize that these window coverings will negatively impact the alarm system’s performance.

Along those same lines and despite the advent of audio glass break testers, it is not always sufficient because they are not being properly used.

Some companies don’t have them, and/or there are other factors that are getting routinely missed by alarm contractors such as window tinting and different types of security film that can also negatively impact upon the catch performance of being able to reliably detect the sounds of breaking glass by an audio glass break detector.

On the other end of the technical spectrum, audio glass break detectors need to be properly placed and tested because a one-size-fits-all approach creates another weakness in the reliability of the sensor functioning as it was designed, intended, and represented to perform.

What You Can Do About It

When determining which windows need audio glass break detection and which ones do not, start off with the premise that all perimeter fixed and sliding glass windows need to be electronically protected with audio glass break detectors and make sure that there are no intervening doors between for example a bathroom window, and where an audio glass break detector is placed by your company.

Another excellent practice is never to try to stretch the detector’s range to its maximum range due to the material fact that it increases false alarms and the propensity that the sensor will not be able to reliably detect and/or miss a forcible glass breakage intrusion event.

To be clear, if you connect to an existing system for “monitoring only,” I recommend performing a security survey and comprehensively evaluating the existing detection scheme. If you find deficiencies, document them and warn the customer in writing.

Have them acknowledge your findings on your approved work order form and/or contract because only discussing it verbally is useless.

Thereafter, provide a recommended action plan and an explanation (again in writing acknowledged by the subscriber) that because of whatever you find, the system will not reliably work and explain why and the costs to address and correct your finding of deficiencies because the last thing that you want to happen is to connect to an existing system that is not reliable, whereby after you started monitoring the account the subscriber suffers an undetected loss.

Suppose the customer does not want to correct the deficiencies. In that case, the alarm contractor needs to strongly consider no longer working with that subscriber because what is worse than no security is a false sense of security.

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About the Author

Jeff Zwirn

Jeffrey D. Zwirn, CPP, CFPS, CFE, FACFEI, CHS-IV, SET, CCI, FASI&T, MBAT, writes Security Sales & Integration’s “Security Science” column. He is also president of IDS Research and Development, an alarm and security consultation, expert witness and training authority providing nationwide services on all issues related to alarm and security matters. He can be reached at 800-353-0733.

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One response to “The Illusion of Audio Glass Break Detection”

  1. Larry Tracy says:


    did you ever actually test glass break detectors, when I was managing C&K I witnessed many tests in our room of most of the competitive detectors on the market this was in our UL approved test room. Many competitive devices would not detect breaking glass 50 % the time, we in fact detected 97% of the time and the instruction manual’s says to always back up glass break sensors with motion detectors due the variable in installs.
    I have regularly used Honeywell ( ex C&K) glass break detectors in installs and have not had a fail to detect for over 15 years.
    Larry Tracy

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