Originally Posted by
Lonewolf_50
ELTs transmit on 121.5/243/406 MHz. (406 MHz contacts a satellite monitoring system. It uplinks the serial No of the Box which the Satellite authority uses to look up the Regulatory authority, who keep a list of serial no's versus tail nos)
The ELT sends the (programmable) ICAO 24-bit address belonging to the aircraft (same as used for Mode S, TCAS, etc). That's sufficient to identify the aircraft without the need to maintain a separate database of unit serial numbers.