Activate this “bracelet of silence” and Alexa can’t eavesdrop
Last year, Ben Zhao decided to buy an Alexa-enabled Echo speaker for his Chicago home. Zhao just wanted a digital assistant to play music, but his wife, Heather Zheng, was not enthused. “She freaked out,” he said.
Zheng characterized her reaction differently. First, she objected to having the device in their house, she said. Then, when Zhao put the Echo in a workspace they shared, she made her position perfectly clear: “I said, ‘I don’t want that in the office. Please unplug it. I know the microphone is constantly on.’ ”
Zhao and Zheng are computer science professors at the University of Chicago, and they decided to channel their disagreement into something productive. With the help of an assistant professor, Pedro Lopes, they designed a piece of digital armor: a “bracelet of silence” that will jam the Echo or any other microphones in the vicinity from listening in on the wearer’s conversations.
The bracelet is like an anti-smartwatch, both in its cyberpunk aesthetic and in its purpose of defeating technology. A large, somewhat ungainly white cuff with spiky transducers, the bracelet has 24 speakers that emit ultrasonic signals when the wearer turns it on. The sound is imperceptible to most ears, with the possible exception of young people and dogs, but nearby microphones will detect the highfrequency sound instead of other noises.
“It’s so easy to record these days,” Lopes said. “This is a useful defense. When you have something private to say, you can activate it in real time. When they play back the recording, the sound is going to be gone.”
During a phone interview, Lopes turned on the bracelet, resulting in static-like white noise for the listener on the other end.
As American homes are steadily outfitted with recording equipment, the surveillance state has taken on an air of domesticity. Google and Amazon have sold millions of Nest and Ring security cameras, while an estimated one in five American adults now owns a smart speaker. Knocking on someone’s door or chatting in someone’s kitchen now involves the distinct possibility of being recorded.
The “bracelet of silence” is not the first device invented by researchers to stuff up digital assistants’ ears. In 2018, two designers created Project Alias, an appendage that can be placed over a smart speaker to deafen it. But Zheng argues that a jammer should be portable to protect people as they move through different environments, given that you don’t always know where a microphone is lurking.
At this point, the bracelet is just a prototype. The researchers say that they
could manufacture it for as little as $20 and that a handful of investors have asked them about commercializing it.
Other precursors to the bracelet include a “jammer coat” designed by an Austrian architecture firm in 2014 to block radio waves that could collect information from a person’s phone or credit cards. In 2012, artist Adam Harvey created silverplated stealth wear garments that masked people’s heat signature to protect them from the eyes of drones, as well as a line of makeup and hairstyles, called CV Dazzle, to thwart facial recognition cameras.
Woodrow Hartzog, a law and computer science professor at Northeastern University, doesn’t think privacy armor is the solution to our modern woes.
“It creates an arms race, and consumers will lose in that race,” he said. “Any of these things is a half measure or a stopgap. There will always be a way around it.”
Rather than building individual defenses, Hartzog believes, we need policymakers to pass laws that more effectively guard our privacy and give us control over our data.
“Until then, we’re playing cat and mouse,” he said. “And that always ends poorly for the mouse.”