Quote:
Originally Posted by Mazrim
I suppose if you leave your GPS on all the time.
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It won't need the have the GPS on all the time - the battery drain imposed by the GPS chipset is way too great for that.
You can tell when you are changing locations without GPS in a number of ways - joining & leaving wifi networks is one way. While on wifi, you can determine with some accuracy where you are based on IP address. Switching cell towers is another indication to the phone that you've moved. There's also cell triangulation which will locate you, albeit less accurately than GPS.
The iPhone already manages to keep pretty darn good track of where you are without excessive use of the GPS - there was a big outcry when an app was released that allowed you to see the location database it keeps via iTunes backups.
I haven't played with the iOS5 beta's, and I haven't read any discussions of how the feature works (i guess because of NDA's), so it will be interesting to see how tight of a geo-fence it allows you to create (ie. how specific - can it distinguish between my house and a neighbors?), as well as how quickly it recognizes when you've entered or left that fence.