Clive Robinson on Schneier's blog came up with a thorough notion years ago: energy leaks plus "energy gapping" systems. He said if any form of energy or matter could transfer from one system toward anothet device then it should be considered a potential leak. So, you have to physically isolate them then block the whole spectrum practically.
Each new story supports his model. Energy gapping for the win.
Haha. I won't go that far. You just shield from as many forms of sounds, light, EM, etc as you can. Alternatively, build memory and info-flow security into your hardware, do POLA at device level, and use TEMPEST-style hardware. Also, as in EMSEC tents or safes, one can separate security levels into their own shielded cages/racks. Already products for that although not sure if energy gapping is thorough enough.
Each new story supports his model. Energy gapping for the win.