My design many years ago was for "shielded" cables that would stop EM leaks in testing except for frequencies they wouldn't be looking for and especially upon receipt of a signal. Sent it to a bunch of people including in defense to create awareness of the risk. Last forum I posted it on was Schneier's blog during a discussion on hardware subversion. TAO leaked later to reveal RAGEMASTER, a VGA cable modification for leaking monitor signals to emanation attack gear. Independent invention or thieving bastards? (shrugs)
Interesting, though, to see they came up with same solution. Just like old keyboard and pin pad attacks. The user has to enter it (input) or see it (monitor). There are many ways to stop outsiders from getting into that information. So, my idea (and NSA's as well) was to make that raw data come to us in whatever way possible. Simpler methods were available such as cheap bugs at 10Ghz that amateur spectrum tools wouldn't see. However, I found natural emanations to be best risk because (a) they're always there, (b) they often increase for non-suspect reasons, and (c) nobody did detection or defense outside of TEMPEST customers.
It's why I keep advising a damn-near Manhattan project on EMSEC all the way from rooms to COTS components down to automating analysis in synthesis tools for ASIC's. The latter already do it quite a bit for non-malicious interference but the game changes going from designing Murphy's ASIC to designing Satan's. ;) Whatever is produced should bring technical sophistication and cost down dramatically with plenty reusable solutions & reference components.