For many years now, satellite-aided search and rescue notification has been available using personal locator beacons (PLBs). Cospas-Sarsat, as this service is officially known, utilizes geosynchronous and low earth orbit satellites. This results in a couple of limitations — the need to have a direct line of sight to a transmitter (for the former), and the possibility that multiple orbits may be required to independently establish a position (for the latter).
To overcome these issues, a new system is on the way. Medium-Earth Orbit Search-and-Rescue (MEOSAR) will add search and rescue transponders to newer GNSSsatellites, including GPS, GLONASS and Galileo.
The GPS version has been dubbed the Distress Alerting Satellite System (DASS). There are eleven GPS satellites currently carrying proof of concept DASS technology on GPS Block IIF and IIR satellites. The system is slated to go operational on at least some Block III satellites, which are expected to go into orbit starting in 2014.
The first two European Galileo system satellites to test this technology are slated for launch in late summer of this year. Their system should allow a verification message to be sent back to the PLBs, basically letting the injured or lost party know that the distress signal has been received. As shown in the above graphic (source), Galileo appears to be the only system currently slated to offer this sort of capability.
The Russians have launched their first GLONASS-K (third-generation) satellite, which also carries a MEOSAR transponder for testing. Thanks to @PocketGPSWorld for sending me down this rabbit hole!