Comment I looked into writing this stuff a decade ago. (Score 1) 250
I take BART into work and sometimes got a ride home, and sometimes I'd forget to pick up my car. So , I realised that location based alarms were a technically feasable feature using GPS units or the newer cellphones that were location aware - so you'd be able to setup reminders to pick up your car when the bay bridge was crossed, or pick up milk when you entered a supermarket.
Back then there was no iPhone and getting the location info on most phones was just too much trouble so I abandoned the idea after a couple of weeks poking around.