https://www.sciencedaily.com/releases/2019/08/190814105223.htm

Researchers from SMU's Darwin Deason Institute for Cybersecurity found that acoustic signals, or sound waves, produced when we type on a computer keyboard can successfully be picked up by a smartphone. The sounds intercepted by the phone can then be processed, allowing a skilled hacker to decipher which keys were struck and what they were typing.

The researchers were able to decode much of what was being typed using common keyboards and smartphones -- even in a noisy conference room filled with the sounds of other people typing and having conversations.