We have tubes for central heating near the entrace of our house. This allows you to mount the IKEA Tradfri motion sensor there.

Simply print it, and stick it into the back of the motion sensor. It will hold by friction fit. Then press it on a 15mm tube.

Print this in PETG, as it is more flexible and holds shape - also when the tube gets hot (central heating). Do not print in PLA, as they will soon fall off your tube due to creep. ABS should also work.