Your phone's wifi signal can be used to identify your gait (way you walk). Your gait is unique enough that it can be used to identify you. If there is prior video footage of view, it can be matched to that too. Impressive research, scary implications https://nakedsecurity.sophos.com/2019/10/07/wi-fi-signals-let-researchers-id-people-through-walls-from-their-gait/
As has been correctly pointed out to me by @xavierluthi, this technique doesn't require you to have a phone. It uses the perturbation to radio frequency signals that *your body* unavoidably creates just be moving in RF signals. The WiFi is used to generate a RF signal for you to affect, if there is none. But given that many parts of the world are now already covered with WiFi, it raises even further questions regarding privacy implications.
@indie @hummingrain The second one is not something i've heard of! the first one is used in the first chapter or so of Doctorow's Little Brother, but using the "more obvious" video surveillance + gait recognition software (not that obvious, even more so 10 years ago). Both are really neat though, I'd read that :)
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