Wired motion sensor started to give false alarms


Old 03-04-16, 07:28 PM
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Wired motion sensor started to give false alarms

I installed a couple of new wired UTC6540 PIR motion sensors in the basement, they worked fine without any false alarms for about a year and suddenly one of them started to trip. I set it up to give a chime, and it trips every few hours. It seems unrelated to the time of day or the turning on of the heating system.

I am wondering how likely are they to simply go bad or should I look for some non-obvious source of tripping? I already checked that the wiring seems fine and there are no spiders in the sensor.

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Old 03-04-16, 08:17 PM
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if they are in the basement make sure spiders and bugs are not walking across the lens [not just inside].

strap off the zone and listen to see if it might be the board and not the motion.

it has a built-in 3.3k resistor -- is that matched to your system?
Old 03-04-16, 10:08 PM
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Have you made ANY changes in the area that the PIR covers? New fixture, aquarium, plant, curtains? All these and more have caused motion falsing.

The usual reason for a PIR to start intermittently falsing is something in the environment tripping it. I'm not familiar with the UTC6540 PIR in particular, but "Pet immune" is a misnomer: They are pet-resistant at best, and can still be tripped by very small animals up close, like a moth fluttering by a few inches away. I would definitely look for possible causes before replacing the PIR.

If you can't find anything, you might invest a few bucks in a low-end PIR like the Honeywell Aurora, replace the 6540, and see if the falsing persists. (Don't throw away the old PIR, it might be perfectly fine.) If the falsing persists, then the problem is almost definitely environmental (including possible critters)

Now temporarily string a 4-wire cable (22/4) across the room and wire both PIRs in parallel, just for testing purposes. Set the Aurora (or whatever PIR you find, but no cheap Chinese junk) so it covers the same area as the 6540 but is positioned at least 10 feet away from your existing PIR.
Now leave it for a day or more and you should have no falsing. Wired in parallel, both PIRs must trip to trigger the zone, which no small critter or hot/cold spot is likely to do. This configuration almost always eliminates the falsing problem.
See if you can find a way to fish the wire so it isn't strung out in the open, and mount both PIRs permanently. You may never find why it falses, but this configuration can solve it.

EDIT: Almost forgot: What make and model is your control panel?
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