Hard disk platters make a convenient microphone
can come in handy to those three-letter agencies that rewrite your hard disks' firmware anyway:
The team’s latest trick is to turn a hard drive into a microphone. They tapped into the feedback system that helps control the position of the read head above the magnetic disk. When the head is buffeted by sound waves, the vibrations are reflected in the voltage signal produced by the drive’s position sensors. By reading this signal, Fu and his colleagues were able to make high-quality recordings of people speaking near the drive.
In another test, they showed that music played nearby could be recorded with high enough fidelity that the music recognition app Shazam could successfully identify the song. Malicious software could use this technique to record audio and then secretly upload it to a remote site, thus bugging a room without ever planting a microphone.