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by _neil 319 days ago
Might have been audio?

https://phys.org/news/2018-02-power-grid-fluctuations-hidden...
1 comments
3036e4 319 days ago
Sibling comment and article mentioning "Electric network frequency (ENF)" lead to further reading mentioning both audio and visual fluctuations being used.
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_neil 319 days ago
Ah you’re right. Pretty cool.
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