Inspired by Neverdie's small round PIR.
There's a matching PIR hat. I have ordered some PCBs to test this. It uses Fanstel's BC832. It is powered by a CR2450
this is a work in process
Two of the solder pads on the bottom of the BC832 can be soldered to to enable the DC-to-DC converter. Those two holes are drilled on the board to give you access.
I haven't received my boards yet to test.
The battery holder/clip is angled and offset so as not to hit those two pins