If you're arrested in California, data stored on your mobile phone, tablet or other portable computing devices could be seized by police without so much as a search warrant.

That's thanks to a recent decision by the state's highest court, which declared on Monday that any and all expectations of privacy are lost once a defendant is in state custody.

By a vote of 5-2, the court said police may "rummage at leisure through the wealth of personal and business information that can be carried on a mobile phone or handheld computer," according to the dissenting opinion of Justice Kathryn Mickle Werdegar.

Werdegar was joined by Justice Carlos Moreno in opposing the decision.

"The majority thus sanctions a highly intrusive and unjustified type of search, one meeting neither the warrant requirement nor the reasonableness requirement of the Fourth Amendment to the United States Constitution," Werdegar continued. "As a commentator has noted, '[i]f courts adopted this rule, it would subject anyone who is the subject of a custodial arrest, even for a traffic violation, to a preapproved foray into a virtual warehouse of their most intimate communications and photographs without probable cause.'"

The dissenting justices suggested that before rummaging through a suspect's mobile device, police should be required to convince a judge of the likelihood that evidence of a crime would be uncovered.

The majority, led by Justice Ming Chin, disagreed, arguing that decisions by the US Supreme Court in the 1970s, permitting the searches of items seized during arrests, was enough precedent to allow warrantless searches of computing devices.

The majority of justices did give credence to the argument that emerging technology amplifies the invasive nature of such a search, but the concurring voices summarized that it would be up to the nation's highest court to reevaluate its prior decisions.

Though highly disappointing to civil libertarians, the California Supreme Court's move is likely to be received with cheers of approval from software developers that specialize in mobile security. Products like Lookout Mobile Security, available for Android devices, allow remote users to wipe out all data on their smartphone simply by logging into a website.

If such software begins to pose a significant obfuscation to police efforts at probing seized devices, it could also lead to a technological arms race of sorts. Authorities could one day acquire products that can take instant snapshots of a mobile device's internal memory before they can be erased, which would be followed by private industry countermeasures to block that, and so on.

San Francisco Chronicle staff writer Bob Egelko noted that the Ohio Supreme Court reached an opposite verdict at the end of 2009, but they were unable to secure a Supreme Court review.

"The Ohio-California split could prompt the nation's high court to take up the issue, said Deputy Attorney General Victoria Wilson, who represented the prosecution in Monday's case," he wrote.

"This has an impact on the day-to-day jobs of police officers, what kind of searches they can conduct without a warrant when they arrest someone," Wilson was quoted as saying. "It takes it into the realm of new technology."

In other significant Fourth Amendment-related decisions recently, the 3rd Circuit Court of Appeals ruled last month that the Obama administration may not obtain information about a cell phone user's location without a court-issued search warrant. Similarly, Delaware Judge Jan R. Jurden ruled against the warrantless placement of a global positioning system on suspects' vehicles, warning that with the rise and spread of computing power, "an Orwellian state is now technologically feasible."

The California Supreme Court's decision in The People v. Gregory Diaz was available online (PDF).