Awful 4th amendment decision yesterday in California that searching one's cell phone data does not require a warrant, in a time and place where a cell phone is more like a computer than a phone. Ars Technica with the details:

The ruling comes as a result of the conviction of one Gregory Diaz, who was arrested for trying to sell ecstasy to a police informant in 2007 and had his phone confiscated when he arrived at the police station. The police eventually went through Diaz's text message folder and found one that read "6 4 80." Such a message means nothing to most of us, but it was apparently enough to be used as evidence against Diaz (for those curious, it means six pills will cost $80). Diaz had argued that the warrantless search of his phone violated his Fourth Amendment rights, but the trial court said that anything found on his person at the time of arrest was "really fair game in terms of being evidence of a crime." In its review of the case, the Supreme Court held that the Fourth Amendment didn't apply to the text messages on Diaz's cell phone at the time of arrest. The court cited a number of previous cases wherein defendants were arrested with all manner of incriminating objects—heroin tablets hidden in a cigarette case, paint chips hidden in clothing, marijuana in the trunk of a car—which did not require a warrant to obtain. The court said that the phone was "immediately associated" with Diaz's person, and therefore the warrantless search was valid.

Some on the Court sensibly dissented, as Ars Technica sums up, arguing that:

the court majority's opinion would allow police "carte blanche, with no showing of exigency, to rummage at leisure through the wealth of personal and business information that can be carried on a mobile phone or handheld computer merely because the device was taken from an arrestee's person. 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."

Some background on past national precedent on cell phone searches:

The courts have gone back and forth in the past on how much privacy protection should be given to data that can be found on a citizen's cell phone. A Pennsylvania District Court ruled in 2008 that law enforcement must get a warrant before acquiring historical records of a cell phone user's physical movements. The same year, the 9th Circuit Court said that the text messages of a police officer had to meet the standards of a reasonable search before law enforcement could access them. In 2010, however, the US Supreme Court said that government employers have the right to read transcripts of employees' e-mails, IMs, texts, and other communications, and that the Fourth Amendment wouldn't protect them from a government search.

Julian Sanchez's classic 2007 Reason magazine cover story on technology and the 4th Amendment, now more than ever!