There's a new GPS-based satellite messaging device on the
market with the brand name of SPOT. 
Basically this is a handheld GPS receiver that also transmits back to satellites with info that includes the
location and one of three pre-programmed responses (OK, Help, 911). The unit costs about $170 and an annual subscription for
the messaging service costs an additional $10/month or $100/year. Messages sent from SPOT are Emailed to recipients set-up
in advance by each owner (except for the 911 message which is also processed by SPOT's emergency response unit).
The Weak Link
Those people out there who've used GPS units in the mountains know that they don't
always work very well when in valleys or under a lot of trees. Reviews of SPOT that I've read state that this is the big problem
with SPOT--you need to be in a place with a clear view of the surrounding (and overhead) sky and not inside of any buildings,
cars, etc.
Conclusion on SPOT
This GPS-only unit isn't ready for the kind of places hikers in the Smokies and
surrounding areas would be expected to travel while hiking. Read a review by GPS magazine here.
What Does Work? PLB's
Personal Locator Beacons (PLB's) which use a 406 MHz digital transmitter as their
primary method of location are still the emergency locator beacon of choice for hikers in mountainous 
areas where the hiker is likely to
be located in valley areas or with significant tree cover. Beacon location is derived by triangulation (doppler) from signals
received by the overhead satellites. This is the exact same technology in use as Emergency Locator Transmitters (ELT's)
for downed aircraft (since 1990). The newest versions of these PLB's are also equipped with a GPS that can improve the
location accuracy (provided the GPS can get a satellite lock). But even without a GPS satellite lock, all
406 MHz style PLB's work in areas where a GPS-only unit, like SPOT, would not. These areas are typically where
hikers in the Smokies might be traveling. The downside is that these PLB's are very expensive (generally about $500
- $650). The good news is that no annual subscription fee is required to use the locating service. They are used ONLY for
emergencies (no casual messages/position reports possible). Here's where you can read more info about one of the two popular
brands of PLB's: ACR Electronics.
Bottom Line
Real world hikers still do not have an inexpensive option for a
locator beacon system that works reliably when hiking the type of terrain we have here in the Smokies. Hikers who can
afford the expense should consider carrying a 406 MHz PLB--not a SPOT.
