I twice visited a Rescue Coordination Centre, and there is no doubt that ELTs, PLBs, and EPIRBs work, luckily 90% are false alarms. Yet they've saved many lives. Late at night, after a few cold ones , I wonder if they could be improved, I'm imagining an ELT that gets "armed" in cruise, autonomously detects unusual bank angles, AOA, ground speed, sink rates, or combinations thereof (can be done with cheap gyros and GPS), and that can separate itself from an airframe and parachute to the surface of the earth, preferably with a copy of voice and flight recorder data. And then I think, it's not going to happen because it's a solution for a very rare problem, and certification costs would be prohibitive