I think another great contender for the future of SAR is often overlooked - ADS-B out.
By 2020, all aircraft flying in US transponder airspace will have to have ADS-B out. So in a few years, pretty much all of the US aircraft will have that technology, not to mention a lot of other aircraft which fly into the US (my own aircraft included). The great thing of ADS-B is it transmits your position regularly (typically much more frequently than SPOT), and requires no monthly/yearly subscription fees. There are lots of ground stations to pick up signals (look at
https://flightaware.com/adsb/coverage for their current map of feeder sites). Many of those are run by amateurs, but anyone can get involved and more and more people are every day). Also, up here NavCanada is in a joint venture called Aireon to ultimately use ADS-B receivers on satellites to pick up position information anywhere on the globe (
http://www.navcanada.ca/en/products-and ... ads-b.aspx).
We're not quite there yet with regards to universal coverage - in particular, if you're flying in very remote areas where nobody has set up a ADS-B receiver as a feeder site to something like FlightAware, there is still nobody to receive your position reports - SPOT still wins there. But the advantages otherwise are numerous:
1. If you plan on flying in the US, you're going to need the technology in your aircraft anyway. Not that it's inexpensive, but it's an expense that will have to be spent regardless.
2. There are no monthly or yearly subscription fees
3. Coverage right now is already fairly good, though not perfect or global yet. As time goes on there should be more receiving ground stations, and if the NavCanada venture materializes hopefully sometime soon there really will be worldwide coverage. No word on if they plan on making that information publicly available as is done now with the ground stations, but even if they don't, I presume it would still be available to SAR operations.
4. Position information is transmitted every few seconds at most, so SAR regions can be narrowed down significantly.
5. More aircraft utilizing ADS-B out improves functionality for everyone, not just the individual aircraft. Aircraft with ADS-B In can see where other ADS-B equipped aircraft are to help with traffic avoidance. This is true everywhere, though ADS-B In will only show other ADS-B equipped aircraft.. except in the US where the position of everyone tracked by radar is rebroadcast regardless of the equipment they have (plus, weather info to boot).
A disadvantage over ELTs is that ADS-B doesn't transmit a mayday signal if an airplane goes down. But then, neither does SPOT, and at least if a plane goes overdue, the aircraft should be near its last transmitted position. And it doesn't matter if the ADS-B antenna or transmitter is destroyed on impact.
The problem with ELTs is they don't send a signal unless there is an impact, and in many cases they can't after impact. Though they have the advantage in that they signal that a problem actually occurred, that only happens if they work.
A 406 Mhz ELT is better than a 121.5 Mhz ELT, no question. But though I agree that SPOT is a good thing, depending on the locations a person is flying, ADS-B out can be just as effective for tracking if not more so. And the situation should only improve over time.