I use a magnetic mount made by Scosche (there are plenty of other brands; nothing special about this one). I took the belt clip off and stuck the mounting plate on the back of the battery door, although I don't see why you couldn't just stick the plate to the belt clip, instead. I did it that way because I just don't use the belt clip. The plate that I put on the pager is the one on the right in the main photo here:
https://www.amazon.com/SCOSCHE-MAGR...512748086&sr=8-4&keywords=scosche+magic+mount
I have two mounts in the car--one vent clip and one suction cup on the dash. I have a couple of mobile devices, too, so it is nice to have the flexibility to put things in whatever configuration I want.
So far I have not had any problems with the pager (or any other device) falling off the magnetic mount. It seems very secure.