I found this article on computer keyboards to be quite interesting. Apparently USB or PS2 keyboards emanate enough electromagnetic signals that someone with the right equipment can detect it and decode the signals to determine exactly what you are typing.

Think ATM machines. Think public kiosks.

Sure, the tests were done under ideal circumstances for the testers, but the reality is, it’s available. And once available, it’s usually not too far away before someone has a semi-portable model to use.