The justices recognized that this departed somewhat from federal case law. But they relied in part on a United States Supreme Court decision last year that the police could not attach a Global Positioning System to a suspect’s car without a warrant. A cellphone, the New Jersey justices said, was like a GPS device.

“Using a cellphone to determine the location of its owner can be far more revealing than acquiring toll billing, bank, or Internet subscriber records,” said the opinion, written by Chief Justice Stuart Rabner. “Details about the location of a cellphone can provide an intimate picture of one’s daily life and reveal not just where people go — which doctors, religious services and stores they visit — but also the people and groups they choose to affiliate with. That information cuts across a broad range of personal ties with family, friends, political groups, health care providers and others.”

Besides establishing a firmer legal bar for the police to obtain cellphone data, the Supreme Court also remanded the case to the appeals court to determine whether the evidence collected using the cellphone records could be admitted in court under an “emergency aid exception” to the requirement for a warrant.

Last year, the American Civil Liberties Union reviewed records from more than 200 local police departments, large and small, and found that they were aggressively using cellphone tracking data, so much so that some cellphone companies were marketing a catalog of “surveillance fees” to police departments, to track suspects or even to download text messages sent to a phone that had been turned off. Departments were using the information for emergency and nonemergency cases.

Some departments had manuals advising officers not to reveal the practice to the public. Others defended its use. The police in Grand Rapids, Mich., for example, had used a cellphone locator to find a stabbing victim who was in a basement hiding from his attacker.

The law has been slow to keep up. The Florida decision in May rejected the reasoning of a lower court that had based its approval of cellphone tracking on a 1973 United States Supreme Court case that allowed heroin found in a suspect’s cigarette pack to be introduced as evidence. “Attempting to correlate a crumpled package of cigarettes to the cellphones of today is like comparing a one-cell organism to a human being,” the decision said.

Nationally, court decisions about cellphone tracking have considered whether it comports with the Fourth Amendment, which guards against unreasonable searches and seizures. But the justices in New Jersey based their decision on the State Constitution, which affords greater privacy protection. The state court has previously ruled in favor of electronic privacy. In 2008, it said that police had to obtain a subpoena from a grand jury to obtain Internet provider records.

“The inescapable logic of this decision should be influential beyond New Jersey because it makes complete sense as to an individual’s reasonable expectation of privacy,” said Rubin Sinins, who filed a friend of the court brief on behalf of the American Civil Liberties Union and the New Jersey Association of Criminal Defense Lawyers.