In June of 2014, the United States Supreme Court ruled unanimously that--barring a genuine emergency--police need a warrant to search your mobile phone. (The case in question is called Riley v. California.)
But it turns out that this ruling may not be much help to California defendants who experienced a warrantless police search of their cell phone before the Riley case was decided.
Just last week, in the case of People v. Macabeo, the California Court of Appeal ruled that courts need not grant a motion to suppress evidence from a warrantless cell phone search that took place before Riley. (In other words, that evidence is admissible in court against a criminal defendant.)
The reasoning here is that warrantless cell phone searches were legal under California law before Riley was decided. So the police who conducted these searches were acting in "good faith"--not committing a form of police misconduct for which they should be punished by having the evidence thrown out.
This reasoning makes a certain amount of sense. But that's no comfort for criminal defendants who are facing charges based on cell phone searches that would be unconstitutional if they took place today.