It's been a month since MH370 disappeared. Technically, the pings should've stopped by now, but it seems that the black box batteries haven't died yet.
But what really is a black box anyway?
It's a NEON ORANGE rectangular object. The box holds critical instruments, like an altimeter, airspeed indicator, attitude indicator, control positions (as in what the pilot was doing with the plane at that time), time of day, etc.
The second part of the data recorder is the Cockpit Voice Recorder. This thing records that last two hours of audio spoken in the Captain and First Officer's headsets. This recorder was especially useful in determining what happened to American Airlines flight 93 on 9/11/01, when voices besides the hijackers' were heard inside the cockpit, indicating that the passengers had stormed the cockpit.
The third and most important part is the underwater locator beacon. This broadcasts a "ping" or beep that can be detected by instruments on naval vessels and aircraft. That is the only reason we may have a CLUE as to where MH370 is, as we can triangulate different occasions on which the pings were heard.