Ok, this is what happened to me in a similar situation with an EPIRB.

2002 Worrell.
When I took Chris Sawyer's place on the boat, he was big on safety. We had three EPIRB's on the boat, two hand held (one on each person), and one 406 satellite EPIRB (on the boat).

The hand held (121.5mHz) EPIRBs send out a radio signal that is picked up by satellites and APPROXIMATES your position. The 406 EPIRBs have an embedded GPS that sends coordinates along with a serial number to the satellites for a MUCH more accurate location. If you do it right, you register your 406 EPIRB and they know who that serial number belongs to. As soon as they get a signal and serial number, they attempt to contact the owner.

In addition, there is a delay in the transmission of the data from satellite to ground, so rescuers are NOT looking at real time data. However the newer 406's are MUCH more accurate than the old 112mHz ones. I think from what I've read there is an ~1/2 hr delay between signal and the people on the ground getting the data. Estimated guess is that given this is a global system, there are no "dead spots". Since you have to have a minimum of three satellites to triangulate a position for the 121's I would think that satellite coverage is not an issue.

During the second night leg of the '02 Worrell, the 406 fired off. It was EASY to see b/c it had a bright strobe on it and was BLINDING us. It was supposed to only fire if it was submersed a certain depth as well, but... regardless, it went off. I tried to turn it off, but... to no avail. As soon as we hit the beach, I ran to the hotel room and took it apart to disconnect the battery. I immediately tried to contact the Coast Guard via VHF, but ended up having to call them. They had received the broadcast and sent a search flight out. I was told that they received several data points that showed us to be moving at ~25kts to the north in the vicinity of Cape Romane, therefor they guessed it was an accidental firing as the EPIRB was moving at a sustained rate of speed.

Since I had called, confirmed the serial number of the EPIRB and it's status, there was no problem/charges. They did say, however that had I not called, the "case" would have stayed open for an additional 24 hours past the last signal received and another flight might have gone out.