An alarm system is comprised of three basic parts – the control panel (the brains of the operation including the communicator), the siren (the mouth of the system) and the detection devices.  Today we are going to talk about the detection devices, commonly referred to in the industry as sensors.  Many times these names are used in a presentation without proper definition.  Here are definitions of the most common sensors so that when you are talking to an alarm professional, you won’t feel he is talking a language you don’t understand. I am going to list them in no particular order.

Contact                A switch that is used on windows and doors to notify you if they are opened or closed.  Contacts come in many shapes, long and skinny 2 piece designed to be mounted on a window to short and stubby that are designed for door jams.  There are also metal contacts for overhead doors and more risky, vandal prone areas.  These switches, also knows as reed switches, are usually magnetic.  There is a glass tube with metal in it and when a magnet is in close proximity, the switch either allows current to pass or not.  Whether or not the current passes is call either a normally open or a normally closed circuit.  When the magnet is moved away from the switch, the circuit either opens or closes causing a signal to be sent to the alarm panel.  Most contacts used today are normally closed.  This is the most common device, found on windows and doors.  They usually, but not always, come in two pieces, the switch and the magnet.

Motion Detector              A detector that can detect motion of a body in its field of view.  Most motion detectors are passive infrared detectors, that is they measure heat.  If the  room is 70 degrees and a human body enters the space, it will detect that 98.6 degree presence and trip the alarm. This type of device is considered interior protection.

Dual Technology Motion Detectors          A detector with two types of detection.  Both must see activity for the detector to trip and cause the alarm system to go off.  Most dual technology sensors consist of a passive infrared detector and a microwave sensor.

Pet Immune Motion Detectors         Typically a passive infrared detector that processes what it sees through a computer chip.  The size of a human is translated to a infrared image and that information is programmed in.  Since the size and weight of the human is known, an algorithm is written so that anything under a specified size, 25, 30 50 or even 90 pounds can be ignored.  That is why pet immune motion detectors will not detect dogs.

Glass Break Detectors                    They do exactly what their name says, if glass breaks, a microphone tuned to the frequency of breaking glass hears it and sets off the alarm.  Glass break detectors are considered perimeter protection, as opposed to motion detectors which are interior, because they  catch an intruder before they enter the home.  They are very effective protection, and computer technology has made them quite false alarm resistant.

Shock Sensors                   Used around window and door frames, they detect shocks around the opening and set off the alarm.  They come in both passive and active versions, and both are quite effective.

Water Sensors                  These devices also come in active and passive versions.  Strategically placed in areas of the house where water may be present, they can alert you if pipes burst, the water heater gives out or your sump fills above the level it should.  These devices can save thousands of dollars in damage.

Temperature Sensors       They can detect temperature when it rises or drops below certain set points.  Very useful for houses that are empty for prolonged periods of time, when notified you can respond before serious damage is caused by bursting pipes.  These devices come in analog and digital versions.

All these devices come in wired and wireless versions and both are equally reliable and effective.

If you live in Central or Northern New Jersey and would like information on any of the topics discussed above, or if you would like us to perform a Home Safety and Security Audit, absolutely free, please call 800-369-3962 or simply click the link below.

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