Broadside

That's indeed an interesting and noble intention. Besides very needed in several areas of this kind of crazy world.
There is this device sometime ago I found on the Internet that could give you ideas. You'll probably find more by googling "micro gps" tracker.
Micro GPS tracker Hadasa - >
Code:
Please Login or Register to see the links
I don't know who makes it but a deep search might bring some lights.

Regards.