Dr David Maddison just created a detailed article published in Silicon Chip here in AU.
It is all about cyber espionage & bugs, with quite a lot of detail on "The Thing" designed by Leon Theremin and placed in a hand crafted carved timber seal. A type of cavity resonator modulated by acoustic waves, that works by illuminating it at 300MHz. Click on item 4 on the list of articles:
http://www.siliconchip.com.au/Issue/...tober/Contents