What information do you store on your cell phone, and what might the police make of that data?

Well, if you get arrested in California for any reason, police can legally search the contents of your cell phone without first getting a warrant.

This is allowed by a new California Supreme Court ruling - and it applies not just to arrests for suspected involvement in street crime, but any arrests made in California. It doesn't matter whether you mouth off to an officer whom you suspect of racially profiling you for a traffic stop or participate in a protest that is declared an unlawful assembly (such as the Nov. 5 protest following the Johannes Mehserle sentencing announcement), or get nabbed for a parole violation - if you're arrested in California, your cell phone no longer has any secrets.

The ruling was made in a case that involved incriminating text messages and a drug deal in Southern California, but the wording of the court decision applies to any information that might be stored on your phone. This might include:

• Text and photo/video messages sent or received
• Email stored on your phone
• Photos, videos and audio files
• Mobile web browsing history
• Instant message conversation transcripts
• Social media posts
• Contact information for people you know (address book, social media connections or communication apps such as Skype)
• Location data inferred from apps (including your camera)
• Voice call history and possibly voice mail messages received

As well as anything else that might be stored on your phone. This could be used to implicate either you or people you associate with.

Your phone doesn't need to be physically on your person at the time of arrest in order for police to confiscate and search it. It merely needs to be in your proximity (such as in your car). And if police or witnesses see you discarding or concealing your phone prior to arrest, it's still fair game.

If this bothers you, your first line of defense (and a good mobile security practice under any circumstances, especially to protect against identity theft) is to lock access to your phone with a code or pattern. Nearly all phones offer this security feature, but many people either forget to use it consistently or don't bother with it because it seems like a hassle.

"The police can ask you to unlock your phone, and many people will go ahead and do that when requested," Catherine Crump of the American Civil Liberties Union said. "But the police almost certainly cannot compel you to unlock your phone without the involvement of a judge."

Crump noted that so far, it's legally unresolved whether police can copy data from an arrestee's phone for future examination. It's also unresolved whether police can legally search not just the data on your phone, but also log into your online accounts for email or other services from your phone. ("Legally unresolved" means that there is a chance that police might do these things, and they may or may not survive a legal challenge.)

Other helpful mobile security practices to protect your phone are to routinely erase your text messages and clear your web browsing history and call history. Cull your photos and email messages. Log out of crucial apps for services like email or banking when you're done and don't store your passwords for those services on your phone.

Turn off location-tracking services such as GPS whenever you don't need them. (GPS drains battery life, anyway.) In November, the ACLU of Northern California published a guide to privacy considerations for mobile location-based services, including a side-by-side comparison of privacy practices for several popular locative products.

If these measures sound cumbersome, then choose carefully which services you'll use for communicating about sensitive topics and focus on protecting access to those.

Expect the California ruling to be challenged - perhaps in the U.S. Supreme Court. But for now, this is a legal fact on the ground in California.