Questions · Intruder detection
What is a passive infrared detector and where does it fail?
It is the most common detector. It emits nothing: it looks at the heat of the scene split into bands by a lens or a mirror, and it triggers when a warm body crosses from one band to the next.
Its limits come out of that, and they are quite specific. It struggles to see somebody walking straight at it instead of crossing in front of it. It loses sensitivity when the ambient temperature gets close to that of the human body, which in an industrial unit with no air conditioning does happen in August. And it triggers on anything that changes temperature quickly: a heater starting up, a draught of warm air, the sun on the lens, a metal sheet cooling in bursts at dusk.
Most of its problems are solved by where it goes —at the right height, across the likely path and not head-on, not pointing at windows, radiators or west-facing metal doors— and by the right lens for the volume to be covered. It is the detector that depends most on the mounting and the one most often hung wherever there was already a screw.
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A written answer is enough to decide whether it interests you. To know whether it works at your site you have to see it on a real scene, with the image as it is and, on top of it, what the system understands from it. That is on the IRIS Neural website, which is the group's product.