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Monday, September 13, 2010

Buyer’s Guide for Commercial Intrusion (Burglar) Alarm Systems: Part 2 Detection Devices

This is the second blog in a series of blogs to provide a comprehensive guide to designing and selecting the intrusion alarm system that is right for your organization. I have tried to keep this as brand generic as possible. This blog will cover the most common type of detectors that are typically used for an intrusion alarm system.

There are many different types of detectors that can be used with an intrusion alarm system. This blog we will concentrate the discussion on the most common type of detectors used with most systems today; door and window contacts, motion detectors, and glassbreaks detectors.

Door and Window Contacts

Recessed Door Contact
These devices are the first line of defense. When protecting your building all the accessible openings should be contacted. There are a number of different manufacturer’s producing contacts. These units are a magnetic contact and when the door or window is opened an alarm is triggered. They produce contacts that are recessed mounted or surface mounted. They make contacts that are designed for monitoring man doors, rollup doors, windows, roof hatches, safe doors, just about any opening you can think of can be contacted. For high security applications they make biased contact switches that are very difficult to defeat.

Rollup Door Contact

Surface Mount Contact

These devices are typically programmed as either a perimeter point or an entry exit point. When programmed as a perimeter point anytime the door or window is opened with the alarm system active an alarm will be generated immediately. When programmed as an entry exit point a delay is provided to allow for entry in or exit out of the door for disarming or arming purposes.

Glassbreak Detectors

When using glassbreak sensors to protect an occupied building it is very important you select a glassbreak detector proven for this application. Not all detectors are equal. The wrong detector will provide ongoing alarm issues.

Glassbreak detectors are used to provide perimeter protection of a building. They detect an intruder the moment glass is broken. These units are designed to sense the breaking of glass and to trigger an alarm condition. For the majority of applications an acoustic glassbreak sensor is what is mostly used today. These sensors listen for the high frequency of breaking glass and trigger an alarm.

ShatterPro II 5812AW
There are two types of units we typically recommend. For quiet spaces we will use an acoustic sensor such as the GE Security / Sentrol 5812AW (ShatterPro II). This unit can be wall or ceiling mounted and provides up to a 25’ radius of detection. This unit can detect through blinds and light drapes.

ShatterPro Plus
For louder areas (break rooms, entry doors, etc.) we will use the GE Security / Sentrol 5885 (ShatterPro Plus) unit. This dual technology unit is equipped with the acoustical glassbreak sensor as well as an infrared detector. It is designed and rated for occupied space. This unit works as an acoustical glassbreak detector except when it senses the interior presence (infrared detector) of a person then it shunts the glassbreak sensor thus avoiding any interior generated alarms.

We have successfully deployed thousands of these units for the Integrated Perimeter Alarm System as I defined it in Part 1 of this discussion.

The glassbreak detectors are typically programmed as a perimeter point; anytime these units sense glass breaking they go into alarm.

Motion Detectors

Choose your motion detector carefully; quality and reliability do matter. A cheap inexpensive passive infrared detector has a greater likelihood of creating false alarms than does a more expensive dual technology detector.

There are two major classes of motion detectors; the passive infrared detector and the dual technology detector.

The passive infrared looks for a change in heat (infrared) within the field of the detector. The dual technology detector looks for motion (microwave) and heat (infrared) both must be present in order to trigger an alarm condition.

Dual Technology
Motion Detector
These detectors are designed for a specific coverage pattern. Make sure the coverage pattern is adequate for the area you are trying to cover. Installing a 35’ x 30’ unit in a warehouse is not going to provide much coverage. Installing a 90’x70’ will provide much better coverage. Keep in mind that the coverage pattern is clear line of site. These units cannot provide the coverage if they are blocked.

These units are typically programmed at interior followers or perimeter points. An interior follow will allow for a delay if an entry exit delay is first present otherwise it goes straight into alarm. The perimeter detector goes straight into alarm.

Next blog we will discuss outdoor and environmental detectors.