There is a simple apple on the market called Y5 power manager. I've tried several, including Tasked, but this is the best way to go without killing your battery with constant GPS location updates. It uses cell tower location only. Its nit as exact on the location, but if you use wifi mainly in one place or if the places you use it are pretty far apart it works flawlessly.
I think tasker can do this also without the gps locations, but it is a bit difficult. Y5 is so simple it almost seems too good to be true. :)
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