Stealing a password from the sound your laptop makes.

[DetlefK]

http://www.tau.ac.il/~tromer/papers/acoustic-20131218.pdf
(warning: very long read)

A computer makes particular sounds that depend on the software that is running at that very moment. Israeli scientists were able to decipher from those sounds what the computer is actually doing.
By sending a test-E-Mail (encrypted with a public key for GnuPG) to a laptop and recording the sounds that it made upon decoding it, the scientists were able to reproduce the private key the laptop used to decrypt it. It took them just an hour.

This security-leak has already been fixed.
http://security-world.blogspot.de/2013/12/security-dsa-2821-1-gnupg-security.html

It's nevertheless better not to read E-Mails while a stranger's cellphone lies next to your laptop...

[intaglio]

1. Many laptops have microphones

and I think even the loudspeakers can be used to pick up the sounds in and around a computer.