Dual Technology Detectors Versus PIR Detectors

What are they and how do they work?

PIR detectors (Passive Infrared Receiver) have been around for over 25 years now, and during that time have been developed to the point where they are reliable and consistent in there operation, with negligible false alarms. Mirror optic PIR detectors are among the best.

So why would manufacturers have ventured down the “Dual Technology detector path, and how do they work?  As with many things in this world, there is a misconception that cheaper is better.  Maybe with some things, but not motion sensors for alarm systems!  Consequently PIR detectors got cheaper and false alarms increased.  Naturally, the PIR detector was to blame.  Not rteally, but the cheap ones were. 

A Dual Technology Detector combines two different technologies into the one package.

That being a PIR and a Microwave detector.

The logic behind this move it seems is that because they detect movement in two entirely different ways, and both must be triggered at the same time to activate an alarm, there will be fewer false alarms right? Wrong.

A PIR Detector is looking for a rapid change in thermal energy moving across its field of view.

A Microwave Detector on the other hand is looking for a mass moving towards or away from it.

So in theory, in order to trigger it must see something with a thermal signature and a large mass moving within its field of view.

Sounds great, but in practice dual technology sensors create more problems than they solve.

Let me explain.

A dual technology detector can be easily defeated by moving in an arc across the face of the detector (the microwave detector can not see this), or in a straight line towards the detector (the PIR detector can’t see this). So in order to be detected it must see a mass with a thermal signature moving diagonally across its field of view.

In order for this detector to actually detect, it has to have both technologies set to high sensitivity. This leads to a movement detector that is overly sensitive and can actually generate false alarms, not eliminate them.

A microwave detector has in fact an almost limitless range. If they are incorrectly located (looking towards the outside of a building instead of looking in), the microwaves can detect a large mass moving several hundred meters away, such as tucks and cars. They can also see through plaster walls and wooden floors, and detect movement outside the intended area, including fans, running water in plastic pipes. They are also easily reflected off flat metal surfaces, including building insulation into unwanted areas.

This is probably why Microwave detectors on their own have been rejected as a reliable method of detecting intruders.

On the other hand an overly sensitive PIR is just that…sensitive. This can easily lead to a situation where, on a stormy night for example, the PIR half is constantly dropping in and out of alarm due to colds winds. The microwave is being upset by the tin walls of a shed rattling or it sees something it shouldn’t, and when the two occur at the same time….false alarm.

A quality PIR motion detector will always outperform a dual technology sensor. End statement.