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Single or Dual Optic PIRs

PIRs (passive Infra-Red) detectors are the most flexible choice of detection.

There are a couple of things to keep in mind with these detectors:

  • Most driveway alarms use a ‘single optic’ detector. Whilst some ‘single beam’ detectors are advertised as ‘weather proof’ and suitable for external use, they have been designed to simply switch on lighting etc. They are NOT designed for security, as they will false activate in bad weather and cats, dogs, rats and birds etc. will also set them off constantly.
  • When choosing a driveway alarm that will be reliable, ensure the detector is ‘Dual Optic’. Dual Optic means that the detector has two ‘beams’ which have diverging angles. Both beams must be broken at the same time to trigger an alarm. These units should be mounted at 1 meter off the ground.
  • Dual optic detectors are designed for external use and are immune to bad weather and small animals like cats, dogs, foxes, birds etc.
  • PIRs, no matter how expensive are NOT very reliable for detecting cars moving past them, unless the car is moving slowly. This is because the side panels on a car, even one with a warm engine are generally the same as the ambient temperature and unless the car is slow moving, the detector will not pick it up reliably. When moving slowly the exhaust will be a major heat source also.

If you have a regular driveway, say 5 – 6 meters, or people have to make a tight turn in to the driveway, then the detectors will pick up the vehicle. If you have a 200 meter driveway, then it is unlikely unless there is a speed bump at the entrance.

Most people are interested in tracking people moving in and out and so the PIR dual optic detectors are by far the best option.

For a more detailed understanding of single and dual optic PIRs, see our guide.

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