Thanks for the excellent info Doug. I find this stuff really interesting, both the technical aspects and the ingenuity of people creating new services.

Not to be a total wet blanket, but I am not yet convinced that a ham radio and a GPS receiver combo might not be just as useful, and more flexible. I don't think anyone makes one of those yet (RINO is FRS). Of course it requires (simple) licensing and some user knowledge, but the infrastructure is there, worldwide, and free. You don't have to rely on pre-designated people necessarily, plus you get instant feedback on your transmissions. Hams (should) know how to forward emergency info too. Of course this unit would cost more than $150, but it's a one-time cost and you have a generally useful device as well. To go along with your proper PLB that you only use when in distress, not just a spot of trouble.

I can't believe somebody would carry a SPOT in a pre-planned serious use situation and not also have a GPS receiver and a 2-way radio. I may not be looking at this right, but it seems to me some of these subscription low-initial-cost devices are preying on ignorance, and are primarily to give a feeling of safety/security more than actually definitely provide any. Seems to be a common marketing strategy these days for all sorts of goods.

Cynical and skeptical enough for ya?