Reading keystrokes

Clattering keyboards may seem the white noise of the modern age, but they betray more information than unwary typists realize. Simply by analyzing audio recordings of keyboard clatter,computer scientists can now reconstruct an accurate transcript of what was typed, including passwords.
And in contrast with many types of computer espionage, the process is simple, requiring only a cheap microphone and a desktop computer.
Such snooping is possible because each key produces a characteristic click, shaped by its position on the keyboard, the vigor and hand position of the typist, and the type of keyboard used.