Our daughter and "son" used the Spot on their vacation in Colorado hiking some of the fourteeners in October of last year. Being an overbearing parent
of a 29 year old doctor (only child)
we insisted that they get one
. It worked well in that area. It must have a clear view to the sky. It will pinpoint your location within approximately 25 feet. This device sends out a choice of three signals, and all will be forwarded to your e-mail and/or cell phone so that family and friends can track you. One signal is "We are OK". Second, is "We need help", but not life threatening. Third, is 911 which goes through Spot service and they alert the proper authorities.
When said daughter went to Honduras for volunteer medical care, the Spot wasn't reliable, causing concern at times. I know, I'm a "Can't let go daddy".
But when said daughter comes home and tells the story about being chased into the ocean at midnight by a aggressive dog, while walking home alone....well you' get the idea.
Same was true of the Dominican Republic, even though these areas show full coverage. Still was cause for some concern when we didn't get a e-mail positioning from Spot. See above about not letting go
Still this device does has some very good points, especially if you are out hiking in uninhabited places of the great 'ol U.S. of A. For an extra fee Spot will track in close to real time.
We would recommend it too!