In the summer of 1945, at the tail end of World War II, a group of Russian schoolchildren arrived at the residence of the United States ambassador in Moscow—and they came bearing a gift. The Vladimir Lenin All-Union Pioneer Organization 1, a kind of Soviet version of the Boy Scouts, presented a large carved wooden replica of the Great Seal of the United States to U.S. Ambassador Averell Harriman, calling it a gesture of friendship to their wartime allies, the United States.

Harriman hung the wooden plaque in his study at the Spaso House, which served as his residence. But what he didn't know was that the plaque contained a cutting-edge listening device, used by the Soviets to eavesdrop on his conversations whenever they wanted. The plaque hung undetected in the ambassador’s study until 1952—a staggering seven years. It would come to be known colloquially as "The Thing."

The Walls Have Ears

Leon Theremin demonstrating his theremin in 1927
Topical Press Agency/Getty Images

The device was the brainchild of the Russian inventor Léon Theremin. In the U.S., Theremin is best known for his eponymous musical instrument, the theremin, which he invented while working for the Soviet military in 1920. But almost two decades after creating the instrument, Theremin found himself in a Siberian gulag. Once in the prison system, he was conscripted to create high-tech radio listening devices in a secret laboratory.

With his second-greatest creation, The Thing, Theremin nearly upstaged himself. Unbeknownst to casual viewers, the wooden Great Seal of the United States he created was like a sandwich cookie, with a tiny capacitive membrane connected to a small quarter-wavelength antenna—which together acted as a microphone—standing in for the cream filling. Theremin's hidden bug wasn't connected to a battery or power supply; the device only worked when a radio signal of the correct frequency was sent to the device from an external transmitter. This signal came via a van parked nearby that could broadcast a strong radio signal, activating the Thing and allowing the Soviets to eavesdrop, via a radio receiver, on unwittingly broadcasted conversations from within the Spaso House study.

Suspicious Voices

Exterior of Spaso House, the residence of U.S. Ambassador in MoscowU.S. Embassy Moscow, Wikimedia // Public Domain

It was the British who first noticed something was amiss. In 1951, a British radio operator was monitoring Soviet air force radio traffic, in their own bit of espionage, when he recognized the voice of the British Air Attaché. It's not exactly clear what happened next, but the following year, an American listening to military radio traffic picked up a conversation featuring American-accented voices that clearly seemed to come from the Spaso House. A few bug-searching sweeps of the embassy, coordinated with the move-in of incoming U.S. ambassador George F. Kennan in May 1952, turned up nothing. But on September 12, 1952, with suspicions still raised, the State Department's security technicians Joseph "the Rug Merchant" Bezjian and John Ford conducted another search for good measure, knowing that the Soviets sometimes removed bugs and later replanted them.

At Bezjian's directive, Kennan sat at his desk and dictated an important-sounding message to his secretary while Bezjian searched the room with his radio instruments. When he switched on his receiver, he picked up a signal almost immediately. Something was broadcasting Kennan's voice from down in the study, and it was something very close by. Minutes later, the team found just what they were looking for—hanging right on the wall.

That night, Bezjian slept with the device under his pillow so that it couldn't be stolen back by the Soviets. It was shipped to Washington, D.C., the next day to be studied.

Kennan published his memoirs of the period in 1967. In the book, he wrote chillingly about the moment he realized that the Soviets had a microphone in his own private study: "It is difficult to make plausible the weirdness of the atmosphere in that room, while this strange scene was in progress … At this particular moment, one was acutely conscious of the unseen presence in the room of a third person: our attentive monitor. It seemed that one could almost hear his breathing. All were aware that a strange and sinister drama was in progress."

Turnabout Is Fair Play

The U.S. didn't initially confront the Soviets about their discovery, and the device was kept secret from the media for several years. But the word got out in 1960: On May 1 of that year, the Soviets shot down an American U2 spy plane and then called a meeting with the United Nations Security Council, calling the U.S.'s espionage an act of aggression. The Thing was subsequently trotted out to prove that spying went both ways between the countries—and had for years.

By then, however, the device was well-known to British and American espionage agencies. After examining the bug's technology, the Brits were able to improve upon it and develop a listening device codenamed SATYR, which was utilized by the British, American, Canadian, and Australian militaries throughout the '50s.

It's not entirely certain where the Thing is located today. It was handed over to the FBI for analysis soon after its discovery, and at some point its membrane was damaged and had to be replaced. It was then sent to the National Security Agency, but it's not clear what happened after that. (The NSA likes their secrets.) However, there's a very faithful copy on display at the National Cryptologic Museum in Fort Meade, Maryland, along with a detailed exhibit showing exactly how Theremin and his lab built the device.

Unlike the original, handling the replica is encouraged; visitors can open up the wooden cabinet to view the recreated microphone and the resonant cavity inside. It's a way to engage with a particularly bizarre chapter in U.S.-Soviet relations—a time when even though the nations pretended to be friends, it was wise to beware schoolchildren bearing gifts.