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An LAPD helicopter claimed to have ID'ed protesters from above and threatened to "come to your house"
(www.motherjones.com)
This is a most excellent place for technology news and articles.
This first thing you should do when going protesting, is to leave your phone at home.
And cover up your face and any visible tattoos or any other identifying features
Put a rock in your shoe too. Gait identification can be shockingly accurate.
Dune sand walking