ELT's
From what I'm learning about them in my own flight training, they're designed to go off on their own from a gravity switch and they're fairly sensitive. There are procedures in place when you have a bit of a rough landing to tune your radios to the emergency channel to check to see if your ELT got activated by mistake.
I've seen the units and they're by no means a black box. A real crash would do them in. It's sounding more and more like that might have happened. Real shame if that turns out to be the case.
Art