I have only a "dumb" phone (so dumb that the alarm feature works only about 50% of the time), and since most of the places I hike have no cell phone reception, it stays hidden in the car. Maybe I need to rethink this--not a smart phone but at least a newer dumb one with a working alarm? At 3.3 oz, it's probably the lightest option.
May your trails be crooked, winding, lonesome, dangerous, leading to the most amazing view--E. Abbey