Martin Vuagnoux and Sylvain Pasini, researchers from the Lausanne Security and Cryptography Laboratory, published a report detailing their findings. The pair tested 11 common keyboards manufactured from 2001-2008 which were all vulnerable to at least one of their 4 attacks.
“To determine if wired keyboards generate compromising emanations, we measured the electromagnetic radiations emitted when keys are pressed. To analyze compromising radiations, we generally use a receiver tuned on a specific frequency. However, this method may not be optimal: the signal does not contain the maximal entropy since a significant amount of information is lost.”