Might have been audio? https://phys.org/news/2018-02-power-grid-fluctuations-hid... | Hacker News

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		_neil 4 months ago \| parent \| context \| favorite \| on: Hiding secret codes in light protects against fake... Might have been audio? https://phys.org/news/2018-02-power-grid-fluctuations-hidden...

3036e4 4 months ago [–]

Sibling comment and article mentioning "Electric network frequency (ENF)" lead to further reading mentioning both audio and visual fluctuations being used.

_neil 4 months ago | [–]

Ah you’re right. Pretty cool.

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