I came across this paper recently 'mmSpy: Spying Phone Calls using mmWave Radars' which says 'mmSpy performs sensing of earpiece vibrations using an off-the-she

I came across this paper recently 'mmSpy: Spying Phone Calls using mmWave Radars' which says 'mmSpy performs sensing of earpiece vibrations using an off-the-shelf radar device that operates in the mmWave spectrum (77 GHz, and 60 GHz).' There's a video with some audio samples here - https://www.youtube.com/watch?v=EuuXAfIYo04 https://www.youtube.com/watch?v=EuuXAfIYo04 The Ti dev boards are around ~£200 if I recall correctly.