I own a Garmin inReach satellite device. Normally I use it for three things: text communications where there's no cell service, weather reports, and navigation.
The real reason I got one was for a feature I hope to never use: the SOS button. This video is a good real world example of what happens when you push that button.
For me there are two big take aways. First of all it works. The second thing is to make sure you spring for the rescue insurance. Things like copter rides from the back country are expensive.