If arrested, the police can seize your cell phone without a warrant as part of a "search incident to arrest," an exception that dates back to English common law. What is currently being disputed in the courts is whether they then need a warrant to search a mobile device's contents. In part, the reason that the laws regarding a cell phone or a camera may be different from the search and seizure of any other property is that search and seizure happen in reverse when it comes to mobile devices. For example, if the police want to find evidence in your home, they get a search warrant, and that gives them the right to search your home and seize incriminating evidence. But with mobile devices, because they are on your person at the time of arrest and because it is their contents, not the object, that is of interest, police have to seize the devices before they can be searched. As a result, police may be in possession of your device before they have a right to look at it, something that would not happen with a house.
Just yesterday, California governor Jerry Brown vetoed
legislation that would have made it illegal for police to search an
arrested person's cellphone without a warrant. This means that in
California, if you are arrested, police can both seize and search your
device without a warrant. The would-be law was a response to the state's
Supreme Court ruling that allowed police to access any data stored on a
phone, including photos, texts, search history, chats, etc.
The implications for protesters are obvious. As Hanni Fakhoury, a lawyer for the Electronic Frontier Foundation, told CNN,
"California police might decide to arrest you for disturbing the peace,
or illegal camping, and then check your phone and see messages coming
through from organizers."
In contrast, the Supreme Court of Ohio found that the state cannot search a cell phone
without a warrant unless for an officer's safety or to preserve
evidence. Because of the discrepancies among state courts on this issue,
many people thought the Supreme Court would weigh in, but just over a week ago,
the Court denied a hearing. The Court may be waiting for a few more
lower courts to weigh in on the issue before taking its own look.
But even if you are not arrested, that does not mean the police necessarily need a warrant to seize your device. In New York, for example, the scene of the biggest protests, police can seize your device if they have probable cause to believe that you have evidence of a crime and they believe you will destroy it. If you tell them you will not destroy the data, the police do not have to believe you. (The Citizen Media Law Project has put together an excellent guide for people attending -- and particularly for those reporting -- on the events in New York.) New York in general has pretty strong protections against search and seizure, but these laws are quite unsettled and interpretations may vary jurisdiction to jurisdiction, court to court.
For protesters, and particularly for citizen-journalists, the uncertainty of the legal terrain can itself be daunting.