Did my last tour as an MCC operator, albeit ten years ago so I am a bit out of the loop, but dont forget the Geostationary satellites. If a 406 goes off in their footprint then an alert is instantly generated and sent to the relevant MCC. In the case of a UK beacon that would be Kinloss. Obviously with no movement like their low earth orbiting brothers no resolved position can be obtained but Falmouth hold the UK maritime beacon register and the aviation one for 406 beacons was "under construction" when I left. As each beacon has its own unique 15 Hex ID its just a case of checking the database and making sure whatever it is attached to is safe. When a 406 low earth orbiting sat alert appears it is either relayed to the MCC of the country of registration or if its a UK beacon, traced by Kinloss or Falmouth depending on whether its AVIation or MARitime. I remember getting just a Geo alert on beacons in store at Bristows or Scotia at Aberdeen Airport which alerted us and when the orbiting sat hit came through we could identify the individual warehouse it was situated in to assist in shutting it down. The Geosat that provided UK area coverage back then was Goes 8 parked 35,000 km above Brazil to give you some idea of the visibility window it has. Obviously UK beacons picked up by other MCC's with a UK register will be relayed by the relevant MCC and the same tracing action provided.
For remote areas there always used to be two sats I think in "global dump" mode for "over the pole" coverage. They would download as they passed the nearest available LUT ground terminal and the data then distributed. Not perfect as I can remember beacons alerts that were hours old coming through due to the time taken to go over the hump .. but better than nothing.
I work on the rigs now as a Radio Operator and all our 406's have 121.5 homers. I have worked fixed rigs where the 406 has the GPS position embedded into it. The likes of the Brent Bravo for instance aren't going anywhere, and have been rooted to one spot for nearly forty years so it makes sense. But I work mobile rigs which obviously makes that a non starter. We never know where we will be in a month !!
PS .. We miss you Nimrod guys, and we appreciate you helo guys. Me more than most in both categories.