Surgically implanted devices that allow paralyzed people to speak can also eavesdrop on their inner monologue.

That’s the conclusion of a study of brain-computer interfaces (BCIs) in the journal Cell.

The finding could lead to BCIs that allow paralyzed users to produce synthesized speech more quickly and with less effort.

But the idea that new technology can decode a person’s inner voice is “unsettling,” says Nita Farahany, a professor of law and philosophy at Duke University and author of the book: The Battle for Your Brain.