Bracelet-Like Jammer Blocks Smart Speakers, Other Microphones with Ultrasonic Noise

Concerned about the privacy implications of always-on microphones, researchers have created a clever wrist-worn jamming device.

Gareth Halfacree
9 months agoSensors / Security

Researchers at the University of Chicago — spurred into action by a domestic disagreement on voice-activated assistance systems in the home — have developed a wearable jamming bracelet designed to prevent smart speakers, phones, watches, and other microphone-equipped devices from listening in to private conversations.

"We engineered a wearable microphone jammer that is capable of disabling microphones in its user’s surroundings, including hidden microphones," the research team explains. "Our device is based on a recent exploit that leverages the fact that when exposed to ultrasonic noise, commodity microphones will leak the noise into the audible range. Moreover, our device exploits a synergy between ultrasonic jamming and the naturally occurring movements that users induce on their wearable devices (e.g., bracelets) as they gesture or walk.

"We demonstrate that these movements can blur jamming blind spots and increase jamming coverage. Lastly, our wearable bracelet is built in a ring-layout that allows it to jam in multiple directions. This is beneficial in that it allows our jammer to protect against microphones hidden out of sight."

The device itself — a bulky bracelet with ultrasonic emitters at regular intervals and an internal battery for power — came about owing to a dispute over the utility-versus-privacy nature of smart voice-activated assistant systems. "She freaked out," researcher Ben Zhao told the New York Times about his desire to buy an Amazon Echo for their home and his wife, fellow researcher Heather Zheng, disagreeing with the plan. "I said, 'I don’t want that in the office. Please unplug it,'" recalls Zheng. "'I know the microphone is constantly on.'"

The Arduino-powered jammer doesn't interfere with any network connectivity — a move which would fall foul of anti-jamming laws — but instead disrupts the microphone's ability to record by overloading it with noise beyond the frequency of human hearing. The bracelet layout isn't just for show, either: By arranging the emitters in a ring, the jammer works even when the wearer can't pinpoint the location of a microphone.

More information on the project is available in theNew York Times interview, on the University of Chicago website, and in the team's paper on the jammer.

Gareth Halfacree
Freelance journalist, technical author, hacker, tinkerer, erstwhile sysadmin. For hire:
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