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The light in my bathroom is controlled by a radar motion sensor. The idea was that radar based sensors can be hidden inside the lamp itself and thus be invisible (so no sensor, no switch, only the lamp is visible). Unfortunately, since it's a small bathroom and some of its walls are made of plaster, the radar sensor detects movement in the corridor as well, turning the light on every time somebody walks by.

Could the radar motion sensor's detection zone be shaped somehow? As the sensor is located on the ceiling, narrowing the detection cone would do the trick. Unfortunately, the device itself only offers control over the light duration, maximum darkness level when it still activates and the sensor's sensitivity (setting this to a low value helps a bit, but is inconvenient because you have to do an elaborate hand dance to turn the light back on again on longer toilet sessions... and it still sometimes detects people in the corridor).

I tried making a cone out of aluminum kitchen foil, but it didn't seem to work at all. Any other ideas?

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Apparently radar motion sensors are also called microwave motion sensors; I managed to find what appears to be my exact sensor model here: sharkward.com/enproductshow.asp?ID=38 – Gregor Petrin Dec 28 '12 at 7:10
Is moving the detector feasible? Does it detect movement in the hall with the door shut? – The Evil Greebo Dec 28 '12 at 12:52
There's one possible location to move the sensor but I'll probably need the electrician to move it there. Will try after new year's when he can come around. Otherwise the idea is for the sensor to be hidden somewhere so I can't move it around freely. – Gregor Petrin Dec 29 '12 at 22:25
The link you provided says that the reach can be modified from 1m to 8m, is this feasable on yours? – Lima Oct 16 '15 at 3:26
The company probably changed their webpage because the sensor listed at that link currently is PIR and doesn't even look that similar to mine. Otherwise my sensor stopped working over a year ago - I was tweaking it so often that the plastic knobs for setting the sensitivities got disconnected from the electronics. After fixing that and assembling the sensor I must have touched some wires together and the sensor was destroyed in a loud bang as I turned the fuse back on :) – Gregor Petrin Oct 16 '15 at 4:06

The problem is that even if your foil cone changed the radiation pattern of the microwave antenna in the sensor so that it no longer transmits energy in the direction of the wall, some of the other microwave energy in the room is going to be reflected by the surfaces that it hits (and some absorbed or passed through, those surfaces). It's a bathroom, so you probably have mirrors, and they reflect microwaves just as well as they do visible light, adding to the problem.

You may be better off replacing the radar detector with a PIR-based occupancy sensor, either a separate switch or part of the light fixture. If you don't want to change the wiring, there are adapter kits available, and I've also started to see PIRs built into the light bulbs themselves.

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My problem is that a regular PIR doesn't detect presence through glass and I would like the sensor to remain hidden inside the lamp for aesthetic reasons. – Gregor Petrin Dec 29 '12 at 22:27

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