Best intruder alarm movement detectors
It’s a question that is often asked. What is the best movement detector for burglar alarm systems?
A movement detector type must be selected based on the environment to protect. The common types of detectors are PIR and Dualtec.
A PIR is a Passive Infra Red detector. They function by used a pyro element to detect the presence of infra red. A basic DIY type detector is typically a single element device. Meaning the pyro element only has a single detector. Dual element pyros have 2 and Quad elements have 4. There are other versions with 6 or 8 and twin dual element types.
Typically, the more elements the more stable the detector will be with sacrificing catch performance.
To cover a larger area a PIR detector will use a lens to scatter the detection on horizontally and vertically.
This ‘scattering’ is done by use of a Fresnel lens or a specialist mirror. Mirror devices are often perceived as superior as it allows a cleaner IR image.
As a warm target moves in the area of coverage the IR received is seen as voltage by the pyro. The more elements a pyro has the less chance there is that localised false alarm sources affecting all elements of the pyro.
As you can see movement in the protected area shows as a pulse. Detectors often feature a programmable pulse count. If a device is programmed for 1 pulse, then a single pulse will cause the PIR to activate. If sent 2 the PIR will trigger on 2 pulses etc. Use of this feature needs understanding and caution. The more pulses that are programmed the slower the PIR detector will be to detect movement. Intruder alarm service engineers can increase the pulse count to make a detector appear more stable without understanding it will dramatically reduce PIR catch performance.
A PIR is designed to detect the movement of an infra-red source, ie a Human, animal etc. But it isn’t capable of distinguishing between a person and an infra-red source. So Open fires, warm or cool items moving (paper on a notice board mounted above a radiator, curtains or blinds blowing by an open window etc.
For harsher environments not suitable for PIR movement detectors, one would usually opt for a Dual tech movement detector
What is a Dualtech Intruder alarm detector
A dualtech burglar alarm detector combines 2 technologies to detect movement. A dualtech movement detector typically combines a PIR detector and a Microwave detector. A microwave detector is basically a mini radar detector.
A microwave movement detector detects movement by using ‘doppler’ shift. As an item that reflects radio waves moves in the area of protection the radio signal received is of a slightly different frequency. If the item is moving towards the detector the signal is compressed. If moving away the opposite. An easy comparison to understand is the sound of a train horn sounding as it passes you. As it approaches the sound of the horn is compressed and the train passes and moves away the signal is expanded changing the pitch of the horn that is heard.
By combining a Microwave and PIR detector the false alarm causes each type is susceptible to shouldn’t overlap. Ie a microwave is immune to draughts and sources of heat, where a PIR detector would detect this. Another example is water moving in plastic pipes (Rain downpipes for example) can be seen by a microwave detector as it can see through plastics. Also a Microwave movement detector if poorly adjusted can see through windows and doors. Therefore its essential that a Dualtech movement detector is setup to suit the area it is installed in.
Some dualtech movement detectors combine a PIR and an ultrasonic movement detector. An ultrasonic movement detector functions exactly the same as a Microwave movement detector but operates at a much lower frequency. But is affected by draughts.
Various manufacturers make these types of movement detectors. Every professional installer will have preferred brands. Once they love and ones they hate. My personal preferred brands are HKC and Optex.
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Written by James Wilson who is a professional installer at an NSI gold approved installed and has over 30 years experience.
