The 'Sonic Attack' in China May Have Been Clumsy Ultrasonic Eavesdropping, Expert Says

A U.S. diplomat in China has reported unpleasant feelings of pressure and irritating sounds, reminiscent of reports of experiences in Cuba that left 21 U.S. diplomats with brain injuries last year.

“The medical indications are very similar and entirely consistent with the medical indications that have taken place to Americans working in Cuba,” secretary of state Mike Pompeo told lawmakers on May 23.

But these were likely not “sonic attacks”—instead, researchers believe the symptoms can be explained by clumsy efforts to eavesdrop on American embassies and consulates using high-tech listening devices.

In both cases, diplomats reported hearing high-pitched noises and feeling dizzy, suffering from headaches, or being unable to sleep. U.S. officials released a sample of the sound:

The Cuban episode was politically fraught, as the Trump administration used it to justify attempts to end the Obama administration’s policy of normalizing relations with Havana. Cuba blamed the noise on crickets. Some observers speculated about rogue Cuban military operatives, or Russian psychological warfare.

The U.S. government doesn’t refer to these episodes as sonic attacks, in part because the FBI has not been able to establish how they could be performed. In 2017, a State Department spokesperson corrected a reporter who asked about them, replying, “I’m not characterizing it that way. That’s your word. That’s not mine. Twenty-one medically confirmed to have experienced health effects.”

Yet that medical confirmation, from an investigation published in the Journal of the American Medical Association, notes that “a unifying explanation for the symptoms experienced by the U.S. government officials described in this case series remains elusive and the effect of possible exposure to audible phenomena is unclear.”

Spying, not attacking

While sound weapons do exist, a direct attack on an embassy by another state would be a major violation of international law. And that theory wouldn’t explain why officials at the Canadian embassy in Cuba reported similar symptoms despite much better relations with the socialist state.

Kevin Fu, a researcher at the University of Michigan, came up with a more compelling explanation: an interaction between devices emitting ultrasonic sounds too high-frequency for humans to hear—and possibly an interaction between spies and counter-spies.

His work focuses on cybersecurity and internet-of-things devices, which can be manipulated using such signals. For example, hackers can use ultrasonic commands that humans can’t hear to take over voice-controlled devices like Amazon’s Alexa.

Fu and his collaborator Wenyuan Xu, a professor at Zhejiang University in China, as well as her graduate student Chen Yan, examined the sound file released by the U.S. and embedded above. They spotted signs that the noise was being produced not by a single ultrasonic device, but by interactions between two different devices. They were able to generate similar noises to those recorded in Cuba with two ultrasonic devices in their lab.

For example, spies could try to place an ultrasonic transmitter—that is, a listening device—in or near a room containing an ultrasonic jammer used by U.S. officials to try and prevent eavesdropping. In the right circumstances, the transmissions of the two devices could interact, producing painful, high-pitched noises. That would jibe with reports that Americans initially affected were CIA operatives under diplomatic cover.

That said, the same type of sound-inducing interaction could also have come from an array of other devices, from rodent repellers and burglar alarms to security cameras and room-occupancy sensors.

“We don’t know for certain this was the cause,” Fu told IEEE Spectrumin February. “But bad engineering just seems much more likely than a sonic weapon.”