Re: switch off your Wi-Fi...
I use an app called LLama which uses the cell ID to work out where you are. So, in my case, I use it to turn off WiFi when I leave home (an are of about 500m around my home in practice) and turn it on again when I get to work (again, a 500m or so radius of my work).
Not a perfect system but good enough for me.
It runs on Android, I don't know if other versions exist.
Biting the hand that feeds IT
