>3. How precise is it.

I've just been away in the Midlands (UK) and used Google Maps on a mobile for the first time. The triangulation of position was only accurate to about 1500m radius and then would switch between positions quite often. Such info would look much like a user that was moving quite a lot - I expect it could be filtered out but this sort precision (and lack of accuracy) appears common in the UK.

Trends are spotted in the first 48-hour window, in our sample. There is the big open question of validation outside the sample population of course.

By precise, do you mean precision versus recall? The tradeoff depends on what you want to do with the inferences. If you send the analysis to say a nurse or family member (i.e., human in the loop, which we think is the right approach) then recall should be optimized.