Glass break detector
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A glass break detector is a sensor used in electronic burglar alarms that detects if a pane of glass is shattered or broken. These sensors are commonly used near glass doors or glass store-front windows.
Glass break detectors usually use a microphone, which monitors any noise or vibrations coming from the glass. If the vibrations exceed a certain threshold (that is sometimes user selectable) they are analyzed by detector circuitry. Simpler detectors simply use narrowband microphones tuned to frequencies typical of glass shattering, and react to sound above certain threshold, whereas more complex designs compare the sound analysis to one or more glass-break profiles using signal transforms similar to DCT and FFT and react if both the amplitude threshold and statistically expressed similarity threshold are breached. New advances in technology have also led to the use of wireless glass break detectors. Simply put an Acoustical Glass Break Detector (AGBD) is an electronic alarm sensor that is designed to detect the sounds made from the breaking of a glass window. While devices may vary from manufacturer to manufacturer, most typically detect a sound signature. This often includes an inaudible lower frequency or infrasonic sounds along with the sharp, brittle sounds we all commonly hear. The sound sensor needs to identify a special pattern of both frequencies. You have heard it before: The first thing you must do BEFORE installing an AGBD device is to carefully read the installation directions and understand what is expected. While most sound detectors work in a similar manner there can be important variances that need to be observed. Remember, AGBD devices may need to only work once during the course of many years to trigger an alarm system. 
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