We are using a 2-component motion sensor. It is actually just one sensor but it needs an LED next to it. Voja managed to put a shrink-wrap sleeve on it for prototyping but we have to plan something for production. Production that is, a few hundred pieces. It does not make sense to make a plastic injection mold for this, so we will go full on 3D printing.

Since production PCB is going to be black too, the black printed component will blend nicely. Well, at least in paper. Here is a preliminary rendering and you can see how I deliberately let a section of the LED stick out  of the black enclosure. 

After we printed it and tested it (thanks Bruce!), it turns out it is too short. For the sensor to work properly, the sleeve has to block the LED from it almost entirely. At least so that the UV light path does not cross right away. Otherwise, it will keep triggering the light unexpectedly

Back to the drawing board!