Second, SPOT should be used more frequently during the day. ... The units need to be left running AT LEAST 30 minutes to ensure a signal reaches a satellite. If there are any obstructions like high canyon walls, or trees in a forest, then leaving it on much longer (hours) is necessary.
I did leave the SPOT on for ~30 minutes or more at each campsite, but apparently that wasn't enough since some of the messages never got through. I think that's the big disadvantage of the SPOT - there's no feedback to tell you if your message was delivered. If the non-receipt of a message is going to make a family member nervous, that's no good. The InReach seems much nicer in that respect.
If you're going to fall unconscious or die, then I certainly agree leaving constant breadcrumbs is the only way to help SAR, since you won't be able to press the SOS button. I wonder how many accidents fall into that category, though, vs broken limbs, hypothermia, or other incidents where you would be able to press SOS. And if you're hiking with a partner, he can press SOS on his device even if you're unconscious. Maybe I'm way off, but I would guess that emergencies where there's nobody conscious who could press an SOS button are a small fraction of all backcountry emergencies. I'd be interested to see some statistics on this.
Focusing on those "SOS button emergencies", the most important thing to me is that my message actually gets through. The technical design of a PLB tells me it should be much more reliable at sending an SOS to the outside world. Now maybe it's a case where SPOT is 99% reliable for emergencies and a PLB is 99.9%, I don't know. But given my past experience with the SPOT I wouldn't trust it in a life-threatening situation. I don't mean to be preachy or denigrate other people's choices, but I view these devices like a fire extinguisher. The only factor that really matters is how well it works in an emergency situation. This is where I think a PLB shines above the alternatives.
