I thought Fossett had a wristwatch that worked like an ELT? Maybe I was mistaken, but in any case, I doubt that the signal it produces is good enough for anything more than line of sight, probably a lot less than that even.

There are such things as indefinite power storage devices (batteries that don't leak a charge until first use) and potted substrate circuits that can survive being shot out of a cannon, impact the earth, and still transmit a signal.

Someday I think we will have a gamma source transmitter that will constantly send a signal through water, earth, the hull of a ship, lead walls, which someone will be able to monitor. You won't have to worry about it shutting off or having the signal attenuated, but it might not be the healthiest thing to EDC.