Freedom to Tinker summarizes a paper on snooping typed information by analyzing a recording of the typing sounds.
The recovered text gets about 90% of the words right and is said to be "quite readable". While passwords don’t have the same statistical properties as ordinary text, as long as the password-typing is accompanied by enough English-typing the algorithm can come up with a short list of possible passwords, which almost always includes the correct one.
"Sounds let eavesdroppers determine what you're typing" plus "cellphone companies can remotely install software to activate the microphone when the user is not making a call" equals "a creepy feeling up and down my spine".