Microwave Spying — Leon Theremin & “The Thing” [UPDATE : CIA Microwave Cavities on display at the Crypto Museum]

“Theremin did some of his best scientific work while imprisoned by one of the most repressive regimes of the 20th century. This brilliant scientist crossed path with the CIA more than once — to our detriment.”

Benjamin R. Fisher — CIA History staff

“History certainly isn’t averse to irony. Seventy-plus years later, descendents of a device invented by the Soviet Union to eavesdrop on its Western enemies are being flogged in an internal catalog of a U.S. intelligence organization.”

Maurits Martijn — The Correspondent (December 2015)

Clara Rockmore & Leon Theremin. Rockmore was a classical violin prodigy and a virtuoso performer of the “Theremin”, the grandfather of all electronic musical instruments.

May 28 2018 — Once upon a time, the Russians relied for many years on a technology unknown to the Americans to spy on the US ambassador in Moscow. The device — known as “The thing” — was the brainchild of an extraordinary genius: Leon Theremin.

I have long suspected that “Microwave Spying” was still a tool on the shelf of the modern spies. In the aftermath of Snowden’s revelations, Der Spiegel published a catalogue of surveillance technologies used by the NSA and CIA to eavesdrop on foreign spies and diplomats.

And indeed, these documents show that the U.S. Intelligence is using products — with names like LOUDAUTO and ANGRYNEIGHBOR — against foreign embassies. Those devices are generally considered as direct successors of Leon Theremin’s brilliant invention. Follow us on Twitter: @INTEL_TODAY

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UPDATE (October 22 2019) — Following the success of the previous exhibitions Secret Communications 1 & 2, the Crypto Museum has once again teamed up with the Foundation for German Communication in Duivendrecht (near Amsterdam, Netherlands) for a third exhibition: Secret Communications 3. [You can check the details of the exhibition here.]

The poster designed to advertise this third exhibition immediately caught my attention…

RELATED POST: Havana Syndrome — What Are the Frequencies Used by US Intel for Microwave Spying? [2019]

That is right! Although MSM continue to ridicule Microwave spying as science fiction gadgetry, the microwave resonant cavities used by the CIA until late in the 90s will be on display.

“The exhibition will cover the following four main themes:


II. Bugs — This time we will show some unique covert listening devices (bugs) that were used during the Cold War by the Stasi and the CIA. We will also explain the methods of hiding such devices and how sweep-teams were able to track them down.

We are able to give a good impression of the techniques used by the West as well as by the Eastern Block, and will be able to show some exiting examples.

Note that many of the bugs used by the CIA were developed and manufactured by a Dutch company, from the 1950s well into the 1990s.”

Technical details regarding these cavities can be found on this page of the Crypto Museum blog.


Lev Sergeyevich Termen (27 August 1896 – 3 November 1993), or Léon Theremin in the United States, was a Russian and Soviet inventor, most famous for his invention of the Theremin, one of the first electronic musical instruments and the first to be mass-produced.

He also devised the interlace technique for improving the quality of a video signal, still widely used in video and television technology.

His listening device, “The Thing”, hung for seven years in plain view in the United States Ambassador’s Moscow office and enabled Soviet agents to eavesdrop on secret conversations. [Wikipedia]

The Thing, also known as the Great Seal bug, was one of the first covert listening devices (or “bugs”) to use passive techniques to transmit an audio signal. It was concealed inside a gift given by the Soviets to the US Ambassador to Moscow on August 4, 1945.

Because it was passive, being energized and activated by electromagnetic energy from an outside source, it is considered a predecessor of RFID technology.

The Great Seal bug hung in the ambassador’s residential office in Moscow and intercepted confidential conversations there during the first seven years of the Cold War, until it was accidentally discovered in 1952.

Operating principles

The Thing consisted of a tiny capacitive membrane 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 a radio signal of the correct frequency was sent to the device from an external transmitter.

This is currently referred in NSA parlance as “illuminating” a passive device. Sound waves (from voices inside the ambassador’s office) passed through the thin wood case, striking the membrane and causing it to vibrate.

The movement of the membrane varied the capacitance “seen” by the antenna, which in turn modulated the radio waves that struck and were re-transmitted by the Thing.

A receiver demodulated the signal so that sound picked up by the microphone could be heard, just as an ordinary radio receiver demodulates radio signals and outputs sound.

The Great Seal Bug: A Story of Cold War Espionage

It was 1945 and the U.S. and the Soviet Union had at best a tenuous relationship. What was presented as a peaceful and friendly gift turned out to be anything but a gesture of good will.

Soviets gave the U.S. ambassador to the U.S.S.R. a carving of The Great Seal, yet hidden inside, just below the surface, was a listening device that went undetected for years.

The bug was activated only when the Soviets wanted, and they made themselves privy to the most secret conversations within those American walls.

It wasn’t until 1952 that it was discovered, but the U.S. kept the findings under wraps in order to use the technology for their own espionage endeavors. The story was filed away for eight years. Until, the U.S. was caught in the act.


UPDATE (May 27 2019) — Daniel Smith just wrote a piece in The Guardian about the dark side of Washington’s spy museum. One of the pics caught my attention.

Gadget heaven … devices containing hidden surveillance equipment including, bottom left, a shoe with a bug in its heel. Photograph: Saul Loeb/AFP/Getty

Although the article does not discuss Leon Theremin and the “Thing”, the famous Great Seal — which contained a Soviet bugging device — appears to be on display at the Spy Museum. [Can anyone confirm to me that this is the real “Thing” and not a replica?]

I was able to read most of the text — the two notes on the bottom left of the US Seal — describing the device.

The Gift That Kept on Giving

In 1945, a group of Soviet children visited the US Embassy in Moscow and gave the Ambassador an hand carved Great Seal of the US.

It stayed in his office until 1952, when technicians discovered a (word missing — undetectable?) listening device inside.

(Sentence missing)

The Mysterious “Thing”

US technicians dubbed the Great Seal listening device “The Thing”. With no battery or circuits, how dit it transmit? After two months, British Tech Ops finally figured it out.

The Thing was a “passive cavity resonator” activated by a radio beam from an outside source. When people spoke, sound waves entered through tiny holes under the eagle’s beak.

They vibrated a membrane that modulated the radio beam, bouncing it back in an audio signal to the people listening in the van.

A few words about the discovery

The existence of the bug was discovered accidentally by a British radio operator at the British embassy who overheard American conversations on an open radio channel as the Soviets were beaming radio waves at the ambassador’s office.

An American State Department employee was then able to reproduce the results using an untuned wideband receiver with a simple diode detector/demodulator, similar to some field strength meters.

Two additional State Department employees, John W. Ford and Joseph Bezjian, were sent to Moscow in March 1951 to investigate this and other suspected bugs in the British and Canadian embassy buildings.

They conducted a technical surveillance counter-measures “sweep” of the Ambassador’s office, using a signal generator and a receiver in a setup that generates audio feedback (“howl”) if the sound from the room is transmitted on a given frequency. During this sweep, Bezjian found the device in the Great Seal carving.

The Federal Bureau of Investigation set about to analyze the device, and hired people from the British Marconi Company to help with the analysis. Marconi technician Peter Wright, a British scientist and later MI5 counterintelligence officer, ran the investigation.

He was able to get The Thing working reliably with an illuminating frequency of 800 MHz. The generator which had discovered the device was tuned to 1800 MHz.

CIA Secret Research Program

Wright’s examination led to development of a similar British system codenamed SATYR, used throughout the 1950s by the British, Americans, Canadians and Australians.

There were later models of the device, some with more complex internal structure (the center post under the membrane attached to a helix, probably to increase Q). Maximizing the Q-factor was one of the engineering priorities, as this allowed higher selectivity to the illuminating signal frequency, and therefore higher operating distance and also higher acoustic sensitivity.

The CIA ran a secret research program at the Dutch Radar Laboratory (NRP) in Noordwijk (Netherlands) from 1954 to approximately 1967 to create its own covert listening devices based on a dipole antenna with a detector diode and a small microphone amplifier. The devices were developed under the Easy Chair research contract and were known as Easy Chair Mark I (1955), Mark II (1956), Mark III (1958), Mark IV (1961) and Mark V (1962). [Wikipedia]

According to Wikipedia:

Although initially they could not get the resonant cavity microphone to work reliably, several products involving Passive Elements (PEs) were developed for the CIA as a result of the research.

In 1965, the NRP finally got a reliably working pulsed cavity resonator, but by that time the CIA was no longer interested in passive devices, largely because of the high levels of RF energy involved.

This last statement is of course utter non-sense. Snowden revelations include a very much ignored information regarding an Audio-based RF retro-reflector — codenamed LOUDAUTO — which provides room audio from targeted space using radar and basic post-processing.

Based on this information and a few other clues, I was able to guess the frequencies used by the NSA/CIA for microwave spying.

RELATED POST: Havana Syndrome — What Are the Frequencies Used by US Intel for Microwave Spying?

I have also argued that this kind of operations may very well be responsible for the yet unexplained and mysterious Havana Syndrome.

RELATED POST: Havana Syndrome — CBS 60 Minutes : “Foreign Government Targeting U.S. Diplomats With Microwave Weapons”

RELATED POST: Havana Syndrome — Dr Diane DiEuliis : “Neuro Science & Technology as Weapons”


Leon Theremin – CIA NEMESIS — CIA official website

White House faces criticism over Russian photographer in Oval Office — Guardian


Microwave Spying — Leon Theremin & “The Thing”

Microwave Spying — Leon Theremin & “The Thing” [UPDATE : Great Seal on display at the Spy Museum]

Microwave Spying — Leon Theremin & “The Thing” [UPDATE : CIA Microwave Cavities on display at the Crypto Museum]

This entry was posted in CIA, Russia, Theremin and tagged , , , , . Bookmark the permalink.

1 Response to Microwave Spying — Leon Theremin & “The Thing” [UPDATE : CIA Microwave Cavities on display at the Crypto Museum]

  1. vesalahde says:

    what about microwave torture, felt murderous frequencies (some remote technique anyway) in 3 finnish cities, Helsinki, Rovaniemi and Oulu


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