During the Cold War, the Soviets built a key tracker for a typewriter. They stuffed tiny electronics in the metal bar that pinches the paper to the roller. The circuits measured the electro-magnetic field produced when rotating the ball to the requested character. When the buffer in the bar was full, it would send a message to a separate eavesdropping devices that would relay the information to headquarters.
Amazing the lengths that states go to spy on one another. Is there any doubt that a state that can design this eavesdropping device would not be able to break into a computer. Even an email server stored in a bathroom closet.
Read the whole articles on this Ars Technica page.