All CPUs emit electromagnetic signals when they are performing tasks, and the first thing these researchers discovered was that binary ones and zeroes emit different levels. The second thing they discovered is that electromagnetic radiation is also emitted by the voltage fluctuations and that it can be read from up to six meters away. These signals, by the way, are known as side-channels, and they are well-documented in the cryptography field.
via An Airgap Won't Secure Your Computer Anymore | Hacked.
