In July the New Jersey Supreme Court ruled that police generally need a warrant to obtain information about the locations of cellphone users. Less than two weeks later, the U.S. Court of Appeals for the 5th Circuit said just the opposite. The first decision was based on Article I, Paragraph 7 of the New Jersey Constitution, while the second decision was based on the Fourth Amendment to the U.S. Constitution. But those provisions are virtually identical, banning "unreasonable searches and seizures" of "persons, houses, papers, and effects." The crucial difference between the two decisions, writes Reason's Jacob Sullum, is the "third party doctrine," which holds that people have no constitutional right to privacy with respect to information they voluntarily share with others.