If you are going to the protest, here is what the EFF suggests.......
A. If you can avoid carrying sensitive data, then you don't have to worry about it getting pulled off the phone. That can include photos, your address book, application data, and more. If you don't need it for the protest, consider removing it for the duration.
B. If you have access to a temporary phone with only the essentials, that might be a better option. Modern smartphones record all sorts of data, and there may be overlooked sources of sensitive information.
C. Password protect your phone. Password protection can guard your phone from casual searches, but it can still be circumvented by law enforcement or other sophisticated adversaries.
D. Start learning to use encrypted communications channels. Text messages, as a rule, can be read and stored by your phone company or by surveillance equipment in the area. If you and your friends can get comfortable with encrypted communications channels in advance, that can keep prying eyes off your texts while they're in transit.(End-to-end encryption does not protect your meta-data. In other words, using end-to-end encrypted communications will keep law enforcement from being able to read the contents of your messages, but they will still be able to see who you're talking to and when you're talking to them.)
E. Keep control of your phone. You may wish to keep the phone on you at all times, or hand it over to a trusted friend if you are engaging in action that you think might lead to your arrest. In any case, you can set the lock screen to turn on quickly, so that if you do lose control of your phone, nobody else gets access easily...
F. Take pictures and video of the scene. As the ACLU says in a recent Know Your Rights guide, "Taking photographs of things that are plainly visible from public spaces is a constitutional right." Unfortunately, that doesn't stop law enforcement officers from occasionally demanding that protesters stop doing exactly that. If you plan to video a protest, read the whole guide here, courtesy of ACLU.
G. Finally, you may wish to explore options that upload directly to another server. Livestreaming sites, and even social media services, can make sure photos and videos get online before law enforcement officers have a chance to delete them.
H. If placed under arrest you have a right to remain silent—about your phone and anything else. If questioned by police, you can politely but firmly decline to answer and ask to speak to your attorney. If the police ask to see your phone, tell them you do not consent to the search of your device. Again, since the Supreme Court's decision in Riley, there is little question that officers need a warrant to access the contents of your phone incident to arrest, though they may be able to seize the phone and get a warrant later.
I. If the police ask for the password to your electronic device you can politely refuse to provide it and ask to speak to your lawyer. Every arrest situation is different, and you will need an attorney to help you sort through your particular circumstance. Note that just because the police cannot compel you to give up your password, that doesn’t mean that they can’t pressure you. The police may detain you and you may go to jail rather than being immediately released if they think you’re refusing to be cooperative. You will need to decide whether to comply.
J. If your phone or electronic device was seized, and is not promptly returned when you are released, you can file a motion with the court to have your property returned. If the police believe that evidence of a crime is on your electronic device, including in your photos or videos, the police can keep it as evidence. They may also attempt to make you forfeit your electronic device, but you can challenge that in court.As a public service these are the high points. I suggest all please read up from the source provided by the ACLU so together we can keep our police forces accountable to the Constitution. And remember, unlike most foreign protests which we see broadcast around the world, we are guaranteed this right here. So use it. Most people would love to, and can't.... Just take some electronic precautions first...