Having used a SPOT for two and a half years, I'll weigh in on the caveats:
• As with all radio signals, you need line-of-sight to a satellite in the constallation. Understandably slot canyons will be tough because it won't have a full view of the sky. Expect "spotty" service at best.
• If you're under trees, chances are it won't work very well either. The low-power high-frequency signal the device emits just doesn't penetrate well.
• They don't work everywhere on earth, but North America is pretty reliable I've found.
• It'll attempt to send your "OK" three times after getting GPS lock then stop. You should leave it on and transmitting for at least 15 minutes if you really care about the OK message.
• This may seem obvious, but it has to be pointed correctly at the sky... if you're backpacking that can be a pain. If it's sitting on your hood, it's easy. I've left mine lying forgotten on the ground and had to go back for it two or three times, my favorite place is on the hood, since presumably you'll see it before driving off.
• I've had luck using mine through various windshields, but keep in mind jeeps have a more vertical windshield rake than most.
• The batteries last damn near forever if you're not using tracking mode.
• They're awesome in the desert. I typically will use the "other" transmission as "I'm rappelling into this here abandoned mine shaft. If you haven't received an OK message in 12 hours send my coordinates to the San Bernardino Cave Rescue team."
• If you press the red button and the GPS was unable to obtain a lock (slot canyon or whatever) but the unit was able to send a signal (RX satellite directly overhead), GEOS will contact your emergency contacts to see if they know where you are. (long story there.
) So tell people where you're going and let them know to answer their phones if they see weird numbers.
• Their website is unacceptably hard to use.
I consider a Sat phone every year but the SPOT had treated me as well as can be expected for a fraction of the price.
