If you are out in the wilderness a lot or driving lonely stretches of road without cellular signals you can also get a hand-held beacon that can be handy.
I have this one: http://acrelectronics.com/product2.aspx?sku=2898
Here in Arizona (as I'm sure many other places with extensive wilderness) people get lost and in distress a lot. With no cell phone service and no one knowing of their plans (so that they can be reported as "missing" by someone) their first instinct is to set a "signal fire." In somewhere as dry as Arizona that's a very bad idea. A couple years ago someone set a signal fire that ended up destroying 250,000 acres. I realize that when someone's lost they panic but if people just used a little forethought when they go out to the wilderness (like taking a PLB) then things would turn out better for everyone.
It's a naive, domestic operating system without any breeding, but I think you'll be amused by its presumption.