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I'm thinking of installing a motion detector inside an existing recessed fixture over my front door in order to illuminate the stairs and door lock at night. Home Depot sells a small sensor that can be installed between the socket and bulb but nobody has been able to tell me if the frosted glass cover will block the sensor.

marked as duplicate by ThreePhaseEel, Tester101 Dec 30 '16 at 12:05

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IR (infra red) motion sensors are generally housed behind frosted plastic housings. Camera lenses also let infra red light pass through. Assuming yours is an infra red motion detector, frosted plastic or glass will not be a problem. The frosting is there to block your view of the lens and to "smear" the background contrast projected onto the IR sensor such that the IR blob's motion is better detected.

  • 2
    PIRs do work thru plastic, they generally do not work thru glass. Just type "does pir work through glass" into google..... – Tyson Dec 30 '16 at 2:40
  • If, by "glass" you mean a typical window, you'd be correct. However, the OP will be hiding the sensor within a recessed fixture where the sensor will be within millimeters of the glass. I tried an experiment with the motion sensor that was installed at my parent's small condo (in a corner of a living room, facing the front door). With the glass placed directly up against sensor, a red light briefly flashes when motion is sensed, just as if there were no glass in front of the sensor. The sensor fails to detect motion when the glass is more than a few inches away. – Knob Scratcher Dec 30 '16 at 18:48
  • A viable question is how the heat generated by the light affects the sensor once it turns itself off. Presumably, it will take some time to cool back down to ambient temperatures, especially if it's isolated within some recessed fixture. – Knob Scratcher Dec 30 '16 at 18:51

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