* https://hackaday.com/2010/09/25/laser-mic-makes-eavesdroppin...
The "remotely" in the title is no warranted in my view. Of course there may be ways to improve on their results. But so far it seems to me that a highly directional microphone would outperform the radar at any distance. One interesting aspect here is how sensitive the attack is to ambient noise. So maybe sitting close to a target with a radar hidden in headphones, one could glean some words even in a noisy environment like a subway. But I'd still put my money on a microphone performing better in that environment.
Now I wonder whether the attack would work better on headphones. They are smaller and should vibrate more. On the other hand the surface is smaller, so on the whole they might not provide more signal to a radar.
https://news.mit.edu/2024/study-smart-devices-ambient-light-...
Audio is by definition a time varying signal. If you cannot sample it fast enough, the information is gone. The fundamental Nyquist-Shannon sampling theorem has proven the concept of the critical (Nyquist) frequency. There are ways around this in special cases: for band limited signals undersampling is a method to reconstruct them using sampling lower than the critical frequency, and for sparse signals compressed sensing can be used. Real life audio is neither band limited (as sampled by any device on the phone), nor sparse. I think it is a physical impossibility with the current sensors.
https://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampli...
I suppose that at certain radio frequencies human bodies are mostly translucent, while the small metal membrane is still resolvable. When a head of a person covers well the acoustic signal (the phone is at the opposite ear), a microphone is helpless, but a radar us still fairly usable.
if i remember correctly it was a defcon demo and the guy ended up getting hired by facebook.
We already have highly accurate sensors for detecting vibrations a few feet away — EARs!
Seems like laser bounce on the phone’s glassy screen/back would be more effective…