Making Sense of Motion Sensors

Though small in size, proper usage of detector and sensor technology is huge.


Motion detection has become an essential ingredient in traditional electronic security and now it is being utilized in access control and video surveillance systems. With more applications and so many different uses, can there be too much of a good thing? It seems the motion sensor is always the device getting the bad rap. However, an understanding about how these devices fit best in your installations will help them to be less prone to scrutiny.

Motion sensing technology has made huge advances since the introduction of PIR (Passive InfraRed) and MW (MicroWave) technologies. Before the introduction of PIRs and MW sensors, interior protection was attempted with devices such as photoelectric beams and ultra-sonic detectors. Beams created a threshold by sending a light beam to a receiver. They were monitored for interruptions in the beam. Ultrasonics emitted high frequency tones and then would measure for distortion or delayed reflections of the signal. Changes in the reflectivity of the protected area signaled an intruder.

While early ultrasonic and photoelectric beam technologies were relatively primitive and inherently prone to false alarms, dealers had nothing else to use for many installation situations. For example, back in the day, photoelectric beams were popular for flat roofs of commercial buildings, and ultrasonics were just the thing for large, harsh environments such as factories and garages. Unfortunately, roof tops are frequented by birds and other flying objects, and industrial spaces are home to equipment such as pneumatics and steam heating. All of these objects can generate false alarms.
Though there is still merit to both of these technologies , there are others from which the installer can select for the most appropriate method of providing protection.

When they first appeared, PIRs and MWs represented a major breakthrough for the alarm industry. The technologies have been combined, and the sensing and signal processing have been refined. The variety of selection has increased, making motion detectors and sensors more affordable and deployable for more applications .

Avoiding Problems

In practice, false alarms are the result of a number of issues including user error, poor application engineering, power surges and lightning, and faulty equipment. Of course, it is no surprise if you choose a substandard motion detector, false alarms result. Some dealers also instruct the central to dispatch on undefined signals (or neglect to instruct the central to log only), in case they are legitimate alarm signals which have been garbled during transmission.

In the Security Dealer March 2006 feature, “KEYWORD: SECURITY,” Randall Wang’s analysis indicated that 75% of his company’s false alarms were being caused by the motion sensors. Although initially startling, alarm dealers probably do not find that number that hard to believe, given the large numbers of motion sensors you deploy.

Although many manufacturers make high quality motion sensors, experienced dealers, looking for the latest and greatest features in order to remain competitive, are still somewhat cautious about jumping on the bandwagon when something “revolutionary” appears on the market.

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