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We have a 35X50 shop that was recently built and it is lit with LED lights in the ceiling controlled by a motion sensor switch on the wall by one of the man doors. The switch is not close to the heater, which is hung off the 20 ft ceiling. The shop is fully insulated and is heated by a Calcana infrared natural gas heater (love that heater). During extremely cold weather, we will notice that the lights are on in the shop when there is absolutely nothing in the shop that would be creating motion of any kind. My assumption has always been that the sensor is somehow being impacted by the heater when it cycles on during cold weather. Can motion switches be impacted by temperature changes created by the heater? Maybe just an adjustment to the sensitivity needed?

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  • Better motion detectors like those installed with security systems (and some light switches) will attempt to filter out false positives like "moving hot air blob" and look for a more "concentrated" movement like what would come from a walking person. Some go so far as to say that a dog will not set them off (too small), but a person will (just right).
    – JPhi1618
    Jan 13, 2020 at 19:49
  • if you only need to detect moving things like mammals, microwave radar sensors are a better bet and won't be fooled by heat signatures at all; they detect moving blobs of water. A fan left on in the room will also likely solve your problem by reducing the differential temp of the air masses and getting the PIR sensor "used" to small amounts of mixing and moving thermal drifts.
    – dandavis
    Jan 13, 2020 at 19:50
  • you could also put a timed switch after the PIR, like used for irrigation and outdoor lighting. make sure to allow a handy by-pass for late-night access.
    – dandavis
    Jan 13, 2020 at 19:58
  • Have you considered a combination PIR/ultrasonic motion sensor, or a microwave-based unit for that matter? Dual-sensor units might have an easier time rejecting the IR interference from the heater... Jan 14, 2020 at 0:34

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Absolutely! Most motion sensors are IR (infrared) detectors and they can "see" heated air as it moves. If it moves fast enough it may trick the sensor into thinking that it's a human vs. just heated air. In your case the heater may be hitting the sensor directly with its IR output.

Try redirecting your sensor so that it doesn't pick up heated air output from the heater and can't "see" into the output of the heater.

It may take some experimentation with aiming to find a good spot between ignoring the heater and detecting you.

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