I don't take a phone. Most of the places I backpack, there's rarely reception, often not even at the trailhead. The one time I tried using my phone as an alarm (car-camping in Yosemite), the battery was dead before morning because the phone was using max power all night trying to connect.

It looks as though I'll have to look for a really lightweight travel alarm!
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May your trails be crooked, winding, lonesome, dangerous, leading to the most amazing view--E. Abbey