This…
Protesters, Here's How To Set Up a Cheap Burner Phone
…is an excruciatingly thorough article from The Intercept on how to almost entirely protect your privacy while taking part in a protest or, for that matter, just walking down the street. Almost entirely. Almost.
As formidable as the defenses it describes are, a determined opponent with sufficient funding can still defeat them all, and in fairly shot order, too.
And yet it doesn't even consider other surveillance methods that don't involve a phone.
The point here is, you will not go unnoticed in this world. Your secrets will always be at risk.
You will learn to live that way.