The 406 beacons send the signal to a constellation of satellites which relay your distress signal to a national center. These are more expensive, but don't have associated subscription fees. The second type use commercial sat phone satellites. These are cheaper, but involve sat phone subscription fees. The most popular (maybe the only one) is SPOT. It basically sends sat phone text messages. You can send non-emergency position data that is forwarded through the Internet, or preprogrammed "l'm okay messages. When you hit emergency, SPOT will call your emergency contacts. If they can't get hold of them, they will call the Search and Rescuse agency for the county based upon your GPS location.
Both systems expect reception of your signal in 15 minutes or less.
The first guy I went looking for, that was using a SPOT, was solo hiking the Pacific Crest Trail. He slipped on the trail and rolled his ankle badly. The position provided by SPOT was exact. When we found him he was with a couple hikers that had stopped to help him. Using SPOT rather than having the hikers go for help saved this gentleman 15-18 hours in the wilderness.
Whoops! U answered it already, thanks..!
That is the one I use.
Spot Solo is awesome.