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?