I've been looking at some of the other questions about sensors, but I can't find a solution to my problem.

I have a movement sensor (PIR i presume) that turns on a light when movement is detected.
Annoyingly it turns on without reason; even when noone is in the house.
it is a dome sensor, located in the ceiling, at about 30cm from the light it turns on; I have put some black tape to obscure 50% of the sensor. it's located near 3 doors that are generally closed. There is absolutely no movement near.

what can trigger a PIR sensor aside movement?
Can I somehow fix this?

  • I had an outdoor motion sensor that turned on constantly with fluorescent bulbs installed (but worked OK with incandescents). Not sure of the mechanism of triggering but possible you have the same issue? Also, you could just have a defective one. Commented Feb 10, 2016 at 4:17
  • You might also check the electrical connection where it is wired into. Commented Mar 10, 2016 at 17:26
  • Are you sure there isn't a pet (or kid) doing it? Could stray infrared (like the sun) be coming through a door or window and scattering in the room?
    – wallyk
    Commented Mar 27, 2016 at 5:10
  • I'm positively sure it can't be infrared (happens at night) and we have no pets. I'm thinking power spikes. the sensor turns on one spot and one energy saving bulb (broken from all the switching). I need to follow up on that too. Thanks
    – Brtrnd
    Commented Mar 30, 2016 at 12:10
  • ghosts, without a doubt. Commented Jan 26, 2017 at 17:55

4 Answers 4


Power bumps can cause them to turn on also spiders. There are models that have better circuitry not to trigger for small power bumps and some have sensitivity adjustments these are the 2 nuisance issues I have found.

  • 1
    its not spiders; powerbumps do seem a very probable explanation. I'm trying to find out how to measure that.
    – Brtrnd
    Commented Mar 30, 2016 at 12:08
  • one of the lamps in the circuit burned; since it burned it seems like it stopped being a problem. I guess that means power bumps.
    – Brtrnd
    Commented Jun 14, 2016 at 9:00

These units also detect heat changes. Make sure the HVAC vent isn't blowing warm or cool air onto the detector or into its view of the space.

  • no hvac in our house; in the next room we have the washing/drying machine; but it also turns on when they are not working.
    – Brtrnd
    Commented Mar 30, 2016 at 12:09

Answer: radio frequency being emitted from rodent deterrent sonic wave devices, cb radio, Wifi router, microwave, infrared light (night cameras), laser lights (level laser) baseball radar gun, and all that stuff your neighbours would use just to irritate you because they don't have the balls to ask you to reset the sensitivity of your lights. Also they can just be dinks. Just place (glue/tape) a small metal screen over the sensor for that will block and minimise radio frequency level being transmitted which is affecting your light sensors and other sensors like motion sensor house alarms. You can buy the metal screen at most hardware stores. RF is everywhere, although it is not visible to the naked eye the technology and affordability of such devices (which are widely available in this day in age) to manipulate/alter the functions of motion sensors makes it too easy for pranksters and menaces to alter the normal functions of any motion detectors. Keep a log and install cameras, you may have snoopy neighbours.


I had the same problem. I traced mine to a cheap LED bulb connected to one of the sensors.

A sensor is hooked to 2 par38 led globes. One of the globes was a cheapie from ebay, I took it off and the problem stopped, I ended up just swapping the globes around so this problem globe is further away from the sensor. Now no problem. I doubt it's heat because I had the old par38 globes and they got so hot but didn't cause a problem. Try different globes and see how you go.

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