I've been slowly absorbing all this SPOT, PLB, and SAR talk, never having any experience with any of this stuff myself.

Instead of a device that signals a central office (corporate or government) for rescue, I think I'd want a pair of devices, one of which can signal the other via satellite. I get one, and my emergency contact gets the other. Such an arrangement would allow for a variety of signal plans and could include an 'OK' button (perhaps pressed at regular intervals, so that not pressing the button on time would be the emerency signal.) It seems to me that makers of SPOT devices could expand in this direction relatively easily.