This is a simple case that snaps together for a Wemos D1 Mini and an AM312 PIR sensor. The lid has a spot for a 12mm x 3mm magnet which allows you to magnetically attach the sensor to things to help keep it in place and hidden under things and out of the way. 

Tip: If you have the built-in LED on the Wemos D1 Mini turn on during motion, the PIR dome while shine a dim blue which gives you feedback when it detects motion.