The New York Times – “…Mr. Zhao and Ms. Zheng are computer science professors at the University of Chicago, and …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 high-frequency sound instead of other noises.

“It’s so easy to record these days,” Mr. 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.”