"So they used a remote acoustic sensing system built around a laser Doppler vibrometer (LDV), which measures non-contact vibrations over a wide range. In their

"So they used a remote acoustic sensing system built around a laser Doppler vibrometer (LDV), which measures non-contact vibrations over a wide range. In their tests, they placed a tiny, jewelry-sized, retro-reflective membrane in the ear as a pick-up for the LDV." These sound curious: these are the devices that three letter agencies have used to suss out sound from glass, aren't they? https://en.wikipedia.org/wiki/Laser_Doppler_vibrometer https://en.wikipedia.org/wiki/Laser_Doppler_vibrometer "Security – Laser Doppler vibrometers (LDVs) as non-contact vibration sensors have an ability of remote voice acquisition"