Following copied from online discussion. (Underlining added by me)
On the Malaysia Airlines flight MH370, the Boeing 777; (I've got over 26 years in USAF Air Traffic Control and 5 years with the FAA) , the ELTs never went off.
I'm of the frame of mind the plane landed safely at a bare base under Muslim Brotherhood control.
The "Shoot Down" theory would have activated the (ELT) Emergency Locator Transmitter, and, unless within the first 5 mins of the hour Zulu time, would have been noticed.
Even within the first 5 minutes, satellites would have pinpointed a lat/long location after the 3rd sweep of the ELT.
We don't have the ELT location from the satellite system, so I don't believe it crashed or ditched into the water.
If it was blown up, the ELTs would have been activated and on battery power, they would have "transmitted pings" all the way down to the ground or if into the water all the way down through the water to the bottom.
They would transmit until the batteries run down, normally three days to a week. ELTs have survived many crashes and explosions, because they are designed to do just that.
My first thought of where to look would be any abandoned air strip left by any military in the Phillipeans.