Since a SPOT is connecting to sattelites, not cell towers, it is quite different from a cell phone and can connect in many places where there is no cell signal.

I tend to agree with the respondent above who felt the beacon is probably more reliable for that one life or death message, while the SPOT can provide the daily peace of mind update which the beacon cannot. What I have read regarding the SPOT's reliability led me to rent a PLB for my last week-long solo backcountry ski trip , which took me into an area where very few if any people go at that time of year, so that if I had been injured and unable to travel my chances would have been pretty poor without some way to call for help. I felt the PLB would be the most reliable. It may be that the new version of the SPOT will be superior. It definitely seems like the way to use the SPOT is to sign up for the tracking feature and keep it on all the time you are moving, so that you are sending plenty of messages. That way if some don't get through others will, and you will have left a pretty good track that should help in finding you even if your emergency call does not get through.