On August 4, 1945, William Averell Harriman, United States ambassador to the Soviet Union, received a delegation of the Vladimir Lenin All-Union Pioneers, the Soviet equivalent of the Boy Scouts. As a symbol of cooperation between the two Allied nations during the still-raging Second World War, the Young Pioneers presented Harriman with a gift: a hand-carved wooden version of the Great Seal of the United States. For seven years, the seal sat in the study of Spaso House, the ambassador’s official residence in Moscow. Little did anyone suspect, however, that this supposed gift of friendship was actually a trojan horse, concealing a listening device so sophisticated that it would take the brightest minds in U.S. Intelligence to finally track it down and crack its secrets. This is the story of “The Thing,” the ingenious creation of an unexpected inventor that pioneered a technology we all still use to this day.

Spaso House, a large New Empire-style mansion at Spasopeskovskaya Square in Moscow, was built in 1913 for Russian textile industrialist Nikolay Vtorov. Confiscated by the Bolshevik government following the 1917 Revolution, the house became the official residence of the U.S. Ambassador in 1933, the year the Soviet Union reestablished diplomatic relations with the United States. From the beginning, it was widely known that the Soviet secret service or NKVD – later the KGB – had spies everywhere – so much so that by the 1950s, visitors to Spaso house were given cards reading:

“Every room is monitored by the KGB all of the staff are employees of the KGB. We believe the garden also may be monitored. Your luggage may be searched two or three times a day. Nothing is ever stolen and they hardly disturb things.”

Nonetheless, Ambassador Harriman did not think to have his gift from the Young Pioneers checked for listening devices. This, however, was more the product of haste than imprudence. After all, there was a war on, and with no time for interior decoration, Harriman simply set the wooden seal aside. It was not until some months later that an unknown staffer removed the seal from storage and hung it in Harriman’s study. When, in April 1946, Harriman’s term as ambassador came to an end, he found the seal too large to fit in his luggage and decided to leave it in place for his successor, Army General and later CIA director Walter Bedell Smith. And so the seal remained in place for seven years, only being removed once to have a crack in its rim repaired.

By the early 1950s, the proliferation of electronic surveillance was such that then-ambassador George F. Kennan began ordering regular sweeps of Spaso House by Secret Technical Surveillance Countermeasures or TSCM teams. As part of these sweeps, the Great Seal was twice examined using radio receivers and metal detectors. However, these examinations revealed no wires, power sources, signal emissions, or hidden metal components outside of a few metal screws. The seal was thus declared clean and re-hung on the study wall.

It was not until 1951 that the seal’s dirty little secret was finally revealed – albeit entirely by accident. In that year, a radio operator at the British embassy was monitoring a radio frequency used by the Soviet Air Force when he picked up a conversation between Ambassador Kennan and the British Naval Attaché. Alarmed, he immediately informed U.S. Embassy security officials, who called in two State Department counter-intelligence experts, John W. Ford and Joseph Bezjian. Unfortunately, a sweep of the building using standard detection gear turned up nothing, leading Ford and Bezjian to conclude that the Soviets had removed their surveillance equipment. In late 1952, however, one Major van Latham, an American military attaché stationed at the embassy chancery building, picked up a radio transmission of Ambassador Kennan’s voice. Another frantic search of the building ensued – which once again turned up nothing.

Suspecting that the Soviets were somehow shutting off their surveillance equipment every time a search was conducted, Ford and Bezjian hatched a clever plan. In early September 1952, Bezjian moved into a guest room at Spaso House and remained there for several days, hosting dinners, playing bridge, and generally living the life of a regular houseguest. Finally, on September 12, he arranged for Ambassador Kennan to hold a bogus dictation session in his study. The document to be dictated was an old embassy dispatch full of unimportant, unclassified information which to an uninformed Soviet agent might sound worth collecting. Meanwhile, the embassy personnel officer, Sam Janey, snuck Bezjian’s detection equipment into the house and delivered it to him in the study. As soon as he turned on the detector, Bezjian heard Ambassador Kennan’s voice loud and clear over his headphones. The bug – wherever it was – was operating. As the Ambassador continued to dictate, Bezjian crept silently around the study, probing every nook and cranny with his detector. Finally, he homed in on the Great Seal hanging over the Ambassador’s desk, which he pulled down from the wall. Suddenly, the signal cut out – only to return a moment later. Bezjian laid the seal down on an armchair and scanned it more closely, revealing the signal to be emanating from the eagle’s head. During his scan Bezjian accidentally bumped the seal, causing the signal to cut out again. Fearing his search had been discovered, he quickly informed the Ambassador of his discovery. Suddenly, however, the signal returned, only to cut out a few minutes later – as it turned out, for the last time.

Confident that he had finally located the mysterious embassy bug, Bezjian carefully examined the seal and discovered a seam running around its outside edge. Grabbing a masonry hammer, he began to pry at the seam, aware that the Soviets might have hidden some sort of anti-tampering booby trap inside the seal. But the seal split apart cleanly, and nothing exploded. Yet what Bezjian found inside the seal would prove more explosive than any bomb.

Nestled in a small cavity carved into the back of the seal was a device unlike any Bezjian had ever seen: a small metal cylinder 20mm in diameter and 17mm long, from which protruded a 23mm-long metal antenna. That was it: no batteries, no wires, no other recognizable components.

Confused, Bejzian and Janey began tearing apart the wall where the seal had hung, searching for the rest of the device. Yet despite working into the small hours of the morning, they found nothing. The entirety of the bug lay inside the wooden seal.

It took weeks of careful analysis by the FBI, CIA, Naval Research Laboratory, and other electronics experts to work out how the alien device worked, and it was more fiendishly clever than the Americans could ever have imagined. The cylindrical copper body of the device was hollow and lined with highly-polished silver plating, forming a carefully-tuned resonant cavity. One end of the cylinder was sealed while the other was covered with an extremely thin silver membrane that acted as a microphone diaphragm. And just a few micrometers below this diaphragm was a mushroom-shaped metal post, machined with small grooves to prevent trapped air from interfering with the device’s operation. Sound waves entering the seal through tiny holes drilled under the eagle’s beak caused the diaphragm to vibrate and distort, varying the distance between it and the metal post and changing the capacitance and capacitance and the transmission frequency of the entire device. Instead of an internal battery, the device was powered by an external 800 MHz radio beam transmitted from a building or van across the street.

This beam caused the device to resonate and transmit its own 1800 MHz signal whose amplitude was modulated by the vibration of the microphone diaphragm, allowing the Soviets to pick up even the faintest sounds in the Ambassador’s study. And since the device only transmitted when “illuminated” by the external radio beam, the Soviets could shut it off whenever they wanted to, making it almost impossible to find using standard radio detection equipment. Its copper and silver construction also made it invisible to regular metal detectors.

Given the ingenious elegance of the device, it is perhaps unsurprising that it sprang from the mind of one of Russia’s greatest inventors: Lev Termen – better known in the West as Leon Theremin.

Born in 1896 in St. Petersburg, Theremin was a physics and engineering prodigy, building his own laboratory and constructing all manner of advanced electrical and scientific devices before the age of 17. After a brief stint as an Army engineer during the First World War and the Russian Civil War, in 1919 Theremin took a job at the Physical Technical Institute in St. Petersberg – then Petrograd – under the great Russian physicist Abram Ioffe. During this time, Theremin developed a radio frequency device for measuring the dielectric properties of gases, which Ioffe encouraged him to develop into an electronic proximity detector and burglar alarm called the “radio watchman.” In 1920, while experimenting with this device, Theremin discovered that the frequency of the radio signal changed as he moved his hand around the antenna. This discovery led to the development of Theremin’s best-known invention: the eponymous, eerie-sounding electronic instrument that is played without touching it. In November of that year, Theremin gave his first public concert with the instrument, and soon thereafter embarked on a musical tour around Europe. Then, in 1928, he moved to the United States and began working with RCA to perfect and market the Theremin.

While the newfangled instrument took the world by storm, influencing all manner of experimental music and producing a few virtuoso performers like Lithuanian musician Clara Rockmore, Theremin’s personal life was less successful. His wife Katia began studying medicine at a school far outside New York City, forcing the couple to see each other only rarely. Then, when Katia became associated with a fascist organization, the Soviet consulate forced Theremin to divorce her to avoid political embarrassment. Theremin eventually married African-American ballet dancer Lavinia Williams, causing him to be ostracized from New York social circles. Finally, in 1938, Theremin abruptly returned to the Soviet Union. While his wife claimed he had been kidnapped, in reality Theremin had fled financial and tax troubles in the United States. But on his arrival in the USSR, he was arrested on suspicion of crimes against the state and imprisoned in Butyrka prison. He was then sent to work in the infamous Kolyma gold mines in Eastern Russia and finally to a sharashka – a secret technical laboratory within the Gulag labour camp system. It was a fate he shared with many other engineers and scientists who fell out of political favour, including aircraft designer Andrei Tupolev and Sergei Korolev, later the architect of the Soviet space program.

While imprisoned in the sharashka, Theremin developed a number of surveillance devices for the NKVD, including a precursor to the laser microphone known as Buran. This used a narrow reflected beam of infrared light to measure vibrations in glass windows, allowing conversations on the other side to be detected. He also developed the endovibrator – the passive radio microphone later used in the Great Seal listening device. In 1947, Theremin was released from the sharashka and awarded the Stalin Prize for his technical contributions. In that same year he met and married his third wife, Maria Guschina. Despite his imprisonment, Theremin continued to develop equipment for the KGB until 1966. In 1956, he was politically rehabilitated as part of Soviet Premier Nikita Khrushchev’s de-Stalinization program.

In 1964, Theremin became a music professor at the Moscow Conservatory, but was thrown out when the administration discovered his association with electronic music, the assistant director declaring:

“Electricity is not good for music; electricity is to be used for electrocution.”

Nonetheless, Theremin continued to experiment with and perform electronic music, and in 1970 became a Professor of Physics in the department of acoustics at Moscow State University. He died in 1993 at the age of 97.

As for the Great Seal Bug, it remained a closely-guarded government secret until May 1960, when its existence was finally revealed to the world. On May 1st of that year, an American Lockheed U-2 spy plane was shot down over the Soviet Union, leading to the capture of its pilot, Captain Francis Gary Powers.The incident sparked an international scandal, derailing peace and disarmament talks between the United States and the USSR. In response, on May 26, during a meeting of the United Nations Security Council, U.S. Ambassador Henry Cabot Lodge Jr. produced the Great Seal Bug as proof that espionage between the superpowers was mutual:

“I produced a wooden carving of the Great Seal of the United States which was given by some Russians to the United States Ambassador to the Soviet Union and which hung in his office behind his desk, and which contained an electronic device which made it possible for persons on the outside possessing a certain type of technical device to hear everything that went on. I produced that as a piece of evidence, and it is direct, fresh, authentic evidence, to show the effectiveness and the thoroughness of Soviet espionage.”

The discovery of the Great Seal Bug prompted the CIA to develop its own version of the resonant cavity microphone under the codename Project Easy Chair, which ran from 1954 to 1967. Other Western nations also developed similar technologies, including the United Kingdom and West Germany. But the influence of Leon Theremin’s ingenious design extends far beyond the narrow field of international espionage. The concept of a passive resonator re-transmitting an external radio signal is the basis of today’s Radio Frequency Identification of RFID technology – used in anti-theft tags, identity cards, and hundreds of other devices we commonly use every single day.

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