The Supreme Court released a landmark unanimous ruling last Wednesday limiting the ability of police officers to search a suspect's cellphone. The court found that, unless it's an emergency situation, Fourth Amendment of the Constitution -- which prohibits unreasonable searches -- protects the data carried in mobile phones.

The 9-0 decision was written by Chief Justice John Roberts, who argued that modern cellphones -- including smartphones and older feature phones -- are too interconnected to the personal lives of Americans to be considered anything but a major element protected by the Fourth Amendment.

"Modern cell phones are not just another technological convenience. With all they contain and all they may reveal, they hold for many Americans 'the privacies of life,'" Roberts wrote in the court's opinion. "The fact that technology now allows an individual to carry such information in his hand does not make the information any less worthy of the protection for which the Founders fought.

"Our answer to the question of what police must do before searching a cell phone seized incident to an arrest is accordingly simple," Roberts said. "Get a warrant."

But don't expect the Supreme Court's limitations to impact all law enforcement, because, as Aaron Sankin detailed on the Daily Dot, the United States Customs and Border Protection (CBP) still don't need to consult with a judge before browsing through your smartphone. In fact, there are very few limitations on CBP searches for both non-citizens and U.S. citizens crossing into the U.S. 

In fact, the only limit behind CBP's power to search your electronics comes from 2007 case law, according to Sankin, when a circuit court of appeals found that border agents had to have a "reasonable suspicion" of wrongdoing before conducting a thorough "forensic search," of electronic devices -- which could include breaking into password-protected parts of electronics.

That single precedent says nothing clear about patrol agents taking a cursory look through a smartphone or putting people in holding cells for hours -- with no obligation to tell detained travelers why they're being held or for how long -- while officials wait for their consent to look through their personal smartphone information. And the circuit court precedent only applies in its jurisdiction: Arizona, California, Hawaii, Idaho, Montana, Nevada, Oregon and Washington. CPB agents in all other states need not provide any justification for a search of your devices -- "reasonable suspicion" or not.

Statistics from an ACLU FOIA request show that border searches of electronic devices are not uncommon. For example, between late 2008 and mid-2010, over 6,500 people traveling to and from the U.S. had their electronic devices searched -- half of them being U.S. citizens. Laptops, cell phones, cameras, hard drives, flash drives and even digital media, like DVDs are all fair game, but cell phones were the most commonly searched device in that period. 

"Cell phones differ in both quantitative and a qualitative sense from other objects that might be carried on an arrestee's person. Notably, modern cell phones have an immense storage capacity. Before cell phones, a search of a person was limited by physical realities and generally constituted only a narrow intrusion on privacy. But cell phones can store millions of pages of text, thousands of pictures, or hundreds of videos," Justice Roberts wrote. "A decade ago officers might have occasionally stumbled across a highly personal item such as a diary, but today many of the more than 90 percent of American adults who own cell phones keep on their person a digital record of nearly every aspect of their lives."

Until another legal fight on the Fourth Amendment, cell phones, and the border control's hazy authority reaches the Supreme Court, it's not a good idea to carry any sensitive information on cell phones across the border because that "digital record" of your life is as good as an open book for CBP.