The US Supreme Court unanimously ruled that the police need warrants to search the mobile phones of people they arrest.
The decision will offer protection to the people arrested every year, many for minor crimes who have found coppers searching through their phones looking for something more serious to arrest them on
The ruling applies to searches of tablet and laptop computers and it also might apply to searches of homes and businesses and of information held by third parties like phone companies.
Chief Justice John Roberts writing for the court, was keenly alert to the central role that mobile phones play in contemporary life. They are, he said, "such a pervasive and insistent part of daily life that the proverbial visitor from Mars might conclude they were an important feature of human anatomy".
The defence of the smartphone was based legally on a part of the constitution which was designed to stop the government interfering with the revolutionaries smuggling business.
Chief Justice Roberts wrote that there was a revulsion against "general warrants," which "allowed British officers to rummage through homes in an unrestrained search for evidence of criminal activity.
"The fact that technology now allows an individual to carry such information in his hand," the chief justice also wrote, "does not make the information any less worthy of the protection for which the founders fought."
The Government is not having a good time with its introduction of Big Brother technology and has lost every time it got to the supreme courts.
The courts have long allowed warrantless searches in connection with arrests, saying they are justified by the need to protect police officers and to prevent the destruction of evidence.
Chief Justice Roberts said while the police may examine a mobile to see if it contains, say, a razor blade, he wrote, "once an officer has secured a phone and eliminated any potential physical threats, however, data on the phone can endanger no one".
Police may turn off a phone, remove its battery or place it in a bag made of aluminium foil to stop it being remotely wiped.
Chief Justice Roberts acknowledged that the decision would make law enforcement more difficult but added that "privacy comes at a cost".