The Spot and other location devices are a good concept in theory for civilians....once authorities have been notified of you missing your return time. Missing persons usually aren't considered missing until 24hrs. A lot can happen in that time... like expiration

The military has been using devices like this for years. However for the military, the beacon frq's are monitored 24-7... kinda like Lojack for humans. If the manufactures offered that subscription service to civilians I could consider it a possible "only" tool in the shed for help. But it still doesn't tell them your condition. Also keep in mind once you're reported / considered missing, the time element to dispatch Bravo Company is a factor.
Personally, if I had only one communication tool I could rely 100% on in my backpack it would be my Ham radio. The cell phone can stay in the truck as far as I'm concerned, or, at the bottom of the pack next to the T-P.

There's a grocery list of reasons I got my Ham license years ago and hiking while alone was at the top of the list.
The new Ham radio test's are as easy as 6th grade math test's now days. Children 8yrs. of age are passing easily joining the Ham radio community.
Wilderness + cellphone = 0
Wilderness + Ham radio = 100
You can buy the study book for 20 bucks that covers everything you need to know and in less than a month you'll pass the test. Or as CA5 mentioned, sign up for a class.