I ordered some PIR motion sensors off of the internet (see link below and last photo) to trigger lights in my house. They work very well but I needed a smaller case for one so I designed this case. The circuit board in these units can be removed easily and placed into the one I designed (the green plastic wire connector has two small prongs on it which need to be pulled up to unplug it from the main board and then slipped through the hole on the side. I printed this with support for the rectangular hole and then just punched out the support when it was done printing.

https://www.amazon.com/BQLZR-12V~24V-Automatic-Motion-Lighting/dp/B00EQ20C6K/ref=sr_1_9?ie=UTF8&qid=1478288117&sr=8-9&keywords=pir