Reminds me of an episode of Due South (the tv series about a Canadian mountie working as a detective in Chicago) in which he correctly works out a password from just the sound of someone typing it.

Turns out this is not so far-fetched after all:

"If you have an audio recording of somebody typing on an ordinary computer keyboard for fifteen minutes or so, you can figure out everything they typed."

https://freedom-to-tinker.com/blog/felten/acoustic-snooping-...