Some judges don't buy it. A couple of years ago, a federal court in Pennsylvania said the practice was at odds with both federal law and the Fourth Amendment to the Constitution, which forbids "unreasonable searches and seizures." Cell-phone location tracking, the judge concluded, invades the privacy Americans have a right to expect.
No kidding: It can reveal if someone is having an affair, visiting a gay bar, attending a militia meeting or tea party event, going to an abortion clinic, seeing a psychiatrist, getting treatment for substance abuse, worshiping at a mosque and any number of other activities some people would rather conceal from a government they do not fully trust.
Those on the other side think a warrant requirement would be unreasonable, since a cop doesn't need court permission to follow you down the street on a hunch. But Northwestern University law professor Albert Alschuler says, "There's a big difference between watching you all the time, everywhere you go, and watching you pass by."
Police departments will never have enough cops to physically tail you and millions of other people constantly. But the spread of cell phones makes it possible for law enforcement to conduct endless surveillance on a scale that is both vast and intimate.
Privacy protections can become meaningless if we don't adapt them to new inventions. Today, we take it for granted that the FBI can't listen to our phone conversations without a search warrant. But in 1928, the Supreme Court said the Fourth Amendment did not apply to anyone "who installs in his house a telephone instrument with connecting wires … to project his voice to those quite outside."
Not until 1967 did the court correct that blunder. It ruled that "the Fourth Amendment protects people, not places," including those things a person "seeks to preserve as private, even in an area accessible to the public."
Maybe it still does. Or maybe not.