The ejection seats either have a beacon integral to them or are connected to the pilot's beacon (or both) so that the distress signal is broadcast long before the pilot gets to the ground.
Pilots getting out of jets at Valley and forgetting to disconnect frequently set off their beacons and it wasn't unusual to have to hover around the base in a Wessex to locate the guilty Sqn.
Equally I ended up hovering outside a hangar in S Wales having homed to a PLB signal that was triggered during maintenance of a Harrier seat.