To one of these: Delorme InReach

Advantage over the spot: 2 way communications. This means that not only do you KNOW when an outgoing message or track point has been successfully sent (the Spot sends blind - it does not know if the message got out), but you are also able to receive messages from civilisation. (yes, I know that might be a negative) :)

I have given this gadget a decent workout in the local hills and also used it for a week in the Tasmanian Central Plateau. Worked brilliantly. As luck would have it my home support team suffered a lightning strike nearby which took out our home network and other stuff. I was able to talk them through repairing and restarting the network from the top of Mt Jerusalem (1444m) via InReach SMS. Didn't have to do it from there, just noticed I had incoming messages when we made the Summit.

To use the SMS features, the device supports either iPhone or Android via bluetooth and custom app. That said, it operates in pre-defined message mode without needing a smartphone. Most days, I just send a pre-defined message when I'm breaking and making camp.

Battery life is at least as good as the Spot as well, it's still on the original 2xAA Lithiums and It must be pushing around 100 hours of on-time by now.

Emergency messages use the same infrastructure as Spot.

Mike