The Thing designed by Léon Theremin was very simple by today's standards, but ingenious. It consisted of a tiny capacitive membrane (a condenser microphone) connected to a small quarter-wavelength antenna; it had no power supply or active electronic components. The device, a passive cavity resonator, became active only when 330 MHz radio waves were beamed to the device from an external transmitter. Sound waves caused the microphone to vibrate, which varied the capacitance "seen" by the antenna, which in turn modulated the radio waves that struck and were reflected by "The Thing". A receiver decoded the modulated microwave signal so the sound that the microphone picked up could be heard, in the same way that an ordinary radio decodes modulated radio waves into sound.

Theremin's design made the listening device very difficult to detect, because it was very small, had no power supply or active components, and did not radiate any signal unless it was actively being powered and listened to remotely. These same design features plus the overall simplicity of the device made it very reliable and gave a potentially unlimited operational life. Assuming that the device had never been discovered, it could easily have worked for 50 years or more.

Theremin's device was embedded in a carved wooden plaque of the Great Seal of the United States. On August 4, 1945, Soviet school children presented the bugged carving to U.S. Ambassador Averell Harriman, as a "gesture of friendship" to the USSR's World War II ally. It hung in the ambassador’s Moscow residential office until it was exposed in 1952 during the tenure of Ambassador George F. Kennan. It was then that the existence of the bug was accidentally discovered by a British radio operator who overheard American conversations on an open radio channel as the Russians were beaming radio waves at the ambassador's office. The CIA found the device in the Great Seal carving after an exhaustive search of the American Embassy, and Peter Wright, a British scientist and former MI5 counterintelligence officer, eventually discovered how it worked.

Theremin, in 1919 created an instrument named after him, a radio-sized box that, with a carefully precise wave of the hands over its antennas, produced sounds that Depression-era listeners found uncanny, heavenly, astounding, unsettling or puerile. As composer Albert Glinsky rightly insists in his exhaustively researched and revealing biography, this frequently clumsy instrument was the first foray into the brave new world of electronic music. Essentially a radio-feedback device, it was impossibly sensitive, often screeched out of tune, required ridiculously deft technique while being advertised as the perfect instrument for the musically illiterate, and was plagued with problems from irreducible portamento (gliding) to unvarying tone and timbre. Still, its magic captured the imagination of millions and has since invaded pop culture, from the eerie theme for the 1930's radio show "The Green Hornet" to movies like "Spellbound."

Video Killed the Radio star on a Theremin....