I've been testing one of these for my app development work, and I think it could be useful for some hiking situations:
https://flic.io
It's a little button you can clip to a backpack strap and assign to up to three different functions on a smartphone (using a click, double-click or hold). I have mine set to trigger the shutter in the camera app, so I don't have to take off gloves to take a photo. It could also be used as a counter if you have something you want to count while hiking, or to send a text message with your location. I'm thinking about integrating it into my Elevation Tracker app to drop markers when I start and finish a climb.
It's IP44 rated, so it should handle some rain, but I'm not sure it would handle being out all day in the rain. The battery is supposed to last a year and is replaceable.
Flic buttons
Re: Flic buttons
Interesting product, but at that price I'd expect better than IP44 sealing.