Mentioned in the article is the  passive bug the Soviets used for covert listening in the US embassy in Moscow. Impressive technology for 1945:  <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;The_Thing_%28listening_device%29" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;The_Thing_%28listening_device%...</a>