Burglar Alarm Motion Detectors – How Do They Work?

Roy Stephenson
 


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Interior Motion Detectors are one of the most cost efficient forms of protection currently available and if they are placed correctly, they can provide valuable protection. By strategically placing motion detectors in key areas such as hallways, living rooms, stairwells and entry ways, you can provide excellent protection without having to cover every single window in your home or business.

There are many different types of motion detectors including active and passive infrared, microwave and acoustical type sensors.

Most motion detectors utilize passive infrared technology to detect intruders. Passive infrared detectors do not put out any type of energy. They gauge the temperature of every thing they see and look for sudden changes in temperature. Something warm moving across a cold room or something cold moving across a warm room will set off the motion detector.

A typical passive infrared motion detector will utilize some type of signal processing to analyze motion and reduce false alarms caused by heaters and air conditioners, hot and cold drafts, sunlight, lightning and moving headlights. Specially designed lenses break down the coverage into opposing zones. Normally two or more horizontally opposed zones needs to detect motion in order to cause an alarm. Passive Infrared detectors can have single, dual or even quad detection elements that can greatly reduce false alarms.

Some motion detectors automatically adjust for timing, amplitude and heat signatures to reduce false alarms from small targets such as rodents and small pets while maintaining the catch performance of humans sized targets. Many have changeable coverage patterns to adjust for large rooms, hallways, barriers or pet coverage.

Dual Technology Detectors combine active microwave signals with Passive Infrared in order to reduce false alarms. The active microwave sends out a signal in the 10 GHz frequency that bounces off fixed objects in the room which creates a repetitive reflection that is sensitive to background disturbances.

In some cases the detectors have an intelligent circuit built in that adapts to adjust to certain background disturbances. You should know that unlike passive infrared, microwave signals will go through walls, ceilings, or other hard obstacles and detect motion. Cars driving through the alley, people moving in the next room or even a ceiling fan in an adjacent office will set it off the microwave portion of the motion detector and effectively turn it into a single technology detector. This can be avoided by making careful adjustments to the coverage pattern and walk testing to insure proper coverage.

Ultrasonic or acoustical type motion detectors were widely used in the early 80’s, but have since fallen out of favor. They transmit an ultra-sonic frequency that is way above what the human hear can detect. This frequency is reflected off of fixed objects in the room which then bounce back in a certain pattern. Moving objects disrupt the pattern and set off the alarm.

A problem with these early ultrasonic detectors is that they would actually burn-in a frequency after being in service for a while. Then, if someone moved the objects around in the room where the motion was located, the detector would not clear because the frequencies did not match.

Roy Stephenson is a Security Consultant with over 21 Years Experience Designing and Installing High End Integrated Security Systems. He is currently the VP of Marketing at http://www.Security-Kits.Com and http://www.EZWatchstore.com

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