At work, we have motion-activated sinks. This is great in theory, but the ones we have seem to be pre-set with a very specific focal length. The following picture marks the spout, the sensor, and the approximate range of locations where movement is detected.
It works perfectly. *IF* you contort your wrists and turn your hands back toward yourself, as if you were approaching the sink from the opposite side. In practice, the sink frequently shuts off while washing. In fact, it shuts off fairly quickly after leaving its sensitivity zone. I typically have to trigger it three or four times during a quick hand wash.
The solution that the collective consciousness has arrived at is to move the soap dispenser in front of the sensor. When it works, it works quite well. The motion sensor focuses on the container and continues to run until it hits a maximum timeout (about 30-45 seconds, if you leave it that long). When it does not work, there are several reasons. Sometimes the soap container is too empty or transparent to trigger the sensor. We do not consistently get the same brand of soap so sometimes the soap container does not fit in a way that triggers the sensor. So what do you do?
If you are me, what you do is this: design your own custom sensor-blocking object and manufacture it on your 3D printer.
This is a simple little two-piece print. The pieces snap together — the base and the body — and form a little stand you can move in front of the motion sensor when you are ready to use the sink.