In a landmark 1967 case, the Supreme Court ruled that evidence from a wiretap on a phone booth was obtained unconstitutionally. Despite the public nature of a phone booth, the tap violated the defendant’s privacy under the Fourth Amendment. “Wherever a man may be,” the court explained, “he is entitled to know that he will remain free from unreasonable searches and seizures.”

Fast forward to today, when courts are wrestling with the question of whether new technology requires them to think differently about what is a reasonable expectation of privacy.

In August, three judges on the United States Court of Appeals for the District of Columbia (two conservatives, one liberal) ruled unanimously  and correctly  that police violated the Constitution when they hid a GPS device on a person’s car and tracked his every move without a valid warrant. That person, Antoine Jones, was convicted of conspiracy to distribute crack and cocaine based on the tracking of his Jeep for four weeks.

The way to define what was reasonable for Mr. Jones to regard as private, the court said, is by focusing on what was unreasonable for law enforcement to consider public. “The whole of one’s movements over the course of a month is not constructively exposed to the public,” Judge Douglas Ginsburg said, adding that it “reveals an intimate picture of the subject’s life that he expects no one to have  short perhaps of his spouse.”