In California the rescue people have refered to these as Yuppy 911 devices, because they have gotten many a call out just because someone is cold, or hungry (order McDonalds maybe?) you get the picture. But these truly are a life saving device now priced at $99.00 and because there are some areas that I get into, that cell phone coverage will not get out of, I am getting one of these.
This is based on experience of my area, where my hunting partner and I go. We came out of this area a couple of weekends ago, and there were 7 text message from my wife.... "Are you okay?" "I haven't heard from you" and so on. When I finally called her, I explained that if I don't have cell service I can't just travel the 50 miles back to where I do, just to check messages and so on.
So SPOT has a button that allows you to send a text message to who ever you have put on the list, and then they can actually check Google Live Earth to pin point your location.
Its a safety device, that could save your life or that of some other hunter.
Keep your buttons protected from getting accidently bumped, and there will not be any accidental pushing of the 911 button sending out a false alarm.