sillysi

I want to make a portable pager alarm system. I have a Microscan MP4000 Pager which I want to wire to a 12V car battery that will be in a portable box. There will be a switch to mimick what would of been the cars ignition. The idea is then to have a microwave sensor connected to the MP4000. In theory when I flick the switch the MP4000 should set and then await a trigger of the microwave sensor. Does this sound right? I presume I can earth the MP4000 directly to the battery?