If you are part of the Alexa ecosphere, you could get a 4th or 5th generation Echo Dot and mount it on your ceiling. These devices utilize ultrasound to perform motion detection. They are always on via mains power, they have WiFi / Zigbee capability, and they integrate well with Smartthings.
AND they have a whole lot more functionality than any mere motion sensor.
Mounting it could be a challenge, but this page might give you some ideas on how to proceed:
And there are wall mount brackets for these devices that, with only slight (or perhaps even no) modifications, should allow you to mount them on the ceiling.