Shared here for public benefit.
Before going to a protest, demonstrators or observers should note that their cellphones may subject them to surveillance tactics by law enforcement. If your cellphone is on and unsecured, your location can be tracked and your unencrypted communications, such as SMS, may be intercepted. Additionally, police may retrieve your messages and the content of your phone if they take custody of your phone, or later by warrant or subpoena.
You should probably leave your own phone at home when you do. You don’t want the burner phone and your own showing up on the same towers at the same time. Turn the burner completely off when near home or your personal phone.
That’s good advice as well, but really only important if you’re a long-term PoI. If you’re just arrested for rioting/protesting, it’s probably not essential.