[shabble]

For interesting research here, see: Keyboard Acoustic Emanations Revisited, Li Zhuang, Feng Zhou, J. D. Tygar

http://www.cs.berkeley.edu/~tygar/keyboard.htm

    "We examine the problem of keyboard acoustic emanations.
    We present a novel attack taking as input a 10-minute sound recording of a user
    typing English text using a keyboard, and then recover- ing up to 96% of typed
    characters. There is no need for a labeled training recording. Moreover the
    recognizer bootstrapped this way can even recognize random text such as
    passwords: In our experi- ments, 90% of 5-character random passwords using only
    letters can be generated in fewer than 20 attempts by an adversary; 80% of 10-
    character passwords can be generated in fewer than 75 attempts.