I just came across a great hybrid (depending on the exact use case): The Automatic Pro plugs into a vehicle's OBD-II port, transmits location updates every 20 seconds when the vehicle is in motion, and draws its power from the car.
Yes, it's an "active" tracker, but the $130 purchase price includes "at least" 5 years of 3G data service.
So it's not exactly ...
I feel that Hexiwear is a pretty good platform, although a little expensive. I feel it ticks most of your boxes:
rubber wrist band - check
rugged and robust - not really, but it's enclosed in that wristband
small form factor - check
no builtin aps - check
loading own software - that MCU is fully programmable
sub 50$ (49$) to be exact
You might initially be ...
I am answering my own question, in case it is of any interest to others.
For development, I have found an excellent and extremely cheap solution. In fact, it could probably be used in non-profits. Only for a commercial product would I need to have something custom manufactured, as I can't find a COTS solution (needs to be smaller, more rugged, with a ...
Just came across another option: TrackR are little sub-$30 transponders with a one-year battery life, though apparently they depend on a device running their app to come within 100 feet of the transponder to update its location.