Reminds me of the trick of shining a laser on a window and recording its fluctuations from sound vibrations on the window surface. The linked method is simpler

Reminds me of the trick of shining a laser on a window and recording its fluctuations from sound vibrations on the window surface. The linked method is simpler and uses the LED power level which dips when speakers are operating to correlate to an audio signal. Pretty neat. This would require external speakers and line of sight I assume, but still neat and probably a lot of nation-state or commercial espionage applications.