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Or highspeed cameras being used to discern the minute colour and luminance changes on a window or a material in the target room which occur due to vibrations in the glass or many other materials due to sound in the target room. This allows reproducing sound that occurs in the room without having access to any microphones.

Or using appropiate lenses to "look through" blinds or other materials that have tiny lensing gaps which the typical person regards as not see-through.

Bouncing a laser off a window has been around since AFAICT the 80's. Maybe 70's. And it didn't need a high speed camera.

It's also relatively easy to defend against as well.

Or hack their router to figure out their physical location. Water+microwaves etc.

Or van eck phreaking.

Or sell them tattletale electronics, like ethernet or usb cables.

Or rubber hose em.

Or ask scroogle/fecebook.

Not limited to audio forensics as the article mentions.

That’s an easy one. There’s nothing different between blinking that status LED and sending a transmission over fibre and wiretapping that.