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I bought a motion detector light a few weeks ago. It worked great out of the box, but now its sensitivity has lowered a lot. You need to be really close to it for it to detect motion.

I tried cleaning dust, but it was not dirty.

Is there way to make it more sensitive? If I remove that white plastic that covers the light sensor, will the sensitivity improve?

I know it might make inside electronics dirty, but I don't care about that I can just clean sensor every week.

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    What kind of motion sensor is this, an outdoor security light, or one for a light switch? Is there an adjustment for sensitivity? What's the ambient temperature, has that changed in the past few weeks, and is the sun hitting the sensor directly? – BMitch Sep 29 '13 at 11:07
  • Do you have the instruction manual for this light? Typically these lights have some sensitivity adjustment available on them. If not, return it and buy one that does. – Tom Swifty Sep 30 '13 at 17:17
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Removing the white plastic that covers the light sensor will make the PIR/motion sensor less sensitive/effective. The cover is actually a Fresnel lens, it has a pattern that scatters light in different directions, increasing sensitivity dramatically (e.g. when light passes through a part of the cover that is 0.5mm away from where it was before, it is sent into a different direction, making it appear as if it has moved more than it has).

I would suggest cleaning or replacing the cover (especially if it is old and has become damaged/dull/dirty). Some PIR sensors also have a dial to turn up or down sensitivity.

I know this is an old question, but it may help others.

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The sensitivity of the PIR (Passive Infra Red) Motion sensor depends on the ambient temperature as well as any dust deposited on the surface of the Fresnel lens. If you live in moderate climate zones, a normal PIR sensor may detect a human up to ten feet or even more. On the other hand if your ambient temperature is 30 degree C or higher, the sensitivity drops in direct proportion to the temperature. Thus in tropical climate zones where the ambient temperature is above 35 degree C, the detection range comes down to less than 5 feet.

Some dust particles lodged on the face of the lens block the PIR sensor which affects the range drastically.

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