[planewave]

Theremin (yes, the same) invented a device using an infrared beam directed at windows which was able to capture speech from inside. [1] This is separate from his RF powered Thing bug that was installed in the US Embassy in Moscow. [2]

Similar techniques have been shown using lasers vibrometers to achieve a similar effect.

Both of these are perhaps not visual in the same way as this method in the article. But, do illustrate the long history of non-traditional microphone eavesdropping techniques.

[1]Albert Glinsky (2000). Theremin: Ether Music and Espionage. University of Illinois Press. p. 10. ISBN 9780252025822. Retrieved 2013-12-28. theremin family huguenot.

[2]https://en.wikipedia.org/wiki/The_Thing_(listening_device)

[mhh__]

Peter Wright's book (Spycatcher) about his (story of his) adventures reverse engineering the thing is a good read.

He had another trick of using simple phasing to make cocktail party type problems easier for analysts. Just play it out of phase in each ear and the brain works it out apparently.