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this post was submitted on 09 Sep 2026
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Privacy
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If you aim a laser on a window it can detect the vibrations of sound hitting it. Pretty much the same as placing your ear up against it, except that a laser can do it from far, far away. You can counter this by installing devices on the windows that actively vibrate them, drowning out the sound.
What's interesting with this technique is the sideways applications. I've heard you can use a chip bag to the same effect. Also, apparently you can actually figure out what someone is typing just from the audio. So with just audio you can eventually figure out their computer passwords.
It's also possible to see what's on a monitor's display through processing the EM emissions called Van Eck phreaking.
There's an entire spectrum of similar attacks: https://en.wikipedia.org/wiki/Tempest_%28codename%29
Anything light/thin enough to resonate at vocal frequencies that can reflect a laser (without altering polarization) will work.
I do remember an experiment, using a chip bag, where university researchers were able to extract audio from a video of a chip bag. I believe they were mapping the intensity of the various specular highlights on the bag and playing the audible frequencies. It was muddied and choppy but intelligible.
Even further, your location and time of recording can be roughly estimated based on audio recordings. It's called Electrical Network Frequency analysis. I forget the specifics, but it had something to do with the frequency change of the power grid (the hum of which can be picked up in some audio recordings, or inadvertently captured as noise from the audio equipment). They can take the recording, determine how the frequency shifted during the recording (corresponding to grid conditions at the time of recording) and compare them to historical data from various utility monitoring stations looking for matches. wiki: https://en.wikipedia.org/wiki/Electrical_network_frequency_analysis