Glass break sensors or also known as acoustical sensors are a perimeter device that uses sound to catch burglars trying to break through glass to get into your home. This type of sensors uses an omni directional microphone that hears the sound of breaking glass. The detector mounts in a wall or ceiling and listens to an area approximately 35 feet in all directions. They do not hear through walls or around corners or into a room because the door is open.

Most units today are tuned to react only to the specific frequency of glass breaking. There are some units still on the market that react to any loud noise. Be aware of the environment that you put an acoustical in. Loud music, high background noise levels, ceiling fans or other machinery (can generate harmonics), and very high humidity such as in bathrooms, can adversely affect the performance of sound detectors. Sounds such as lightning cracking, some people’s sneezes, clanking two glasses together in the sink or a pet bird squawking would also replicate this frequency and cause false alarms.

Newer detectors are mostly immune to loud noises unless they are extremely close the frequency of breaking glass. There are even detectors that are designed to only work with certain types of glass and in other cases the type of glass will affect the range and performance of the unit. Most commonly used types of glass for home windows are:

Tempered Glass: Which breaks into rounded grains instead of jagged shards.

Plate Glass: The most common which contains few impurities.

Laminated: Resists shattering, generally a composite of two sheets of glass with an intermediate layer of transparent plastic.

While it’s not easy to find a sensor that can work with only the glass used on your window, it is easier to get one that can work with most common glass such as the MCT501 – Visonic Wireless Glass Break Detector.

A major advantage of these units is their ability for one detector to protect a medium sized room with several windows. With recent development of dual technology sensors, it’s making this type of sensors to be a very reliable detector. Several manufacturers have combined both motion and sound detectors into one unit such as the 71242 PIR DETECTOR that will not trip an alarm unless both technologies have activated. This unit may be used where the normal conditions would cause a single technology detector to generate false alarms or for enhanced false alarm protection.

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