A plane crashes and then the ELT automatically begins sending a signal, ok.
I raised this on the MH370 thread, but we never got an answer.
It is my understanding that there is no requirement for all airliners to have crash ('g') activated ELTs. Many have ELTs in the rear cabin that rely on crew removing and activating them after an accident.
The more modern variants do have (additional) 'g' activated ELTs, albeit the 787 ones were deactivated / removed post the LHR incident, and I do not know if they have been reactivated. Partly comes down to requirements of the country of registration.
So whether the MH370 777 had one I open to ideas?