The ACLU has released thousands of pages of documents to the New York Times that show that local police departments are routinely using cellphone tracking with almost no judicial oversight — and cell phone companies are making a lot of money as a result.

The internal documents, which were provided to The New York Times, open a window into a cloak-and-dagger practice that police officials are wary about discussing publicly. While cell tracking by local police departments has received some limited public attention in the last few years, the A.C.L.U. documents show that the practice is in much wider use — with far looser safeguards — than officials have previously acknowledged.

The issue has taken on new legal urgency in light of a Supreme Court ruling in January finding that a Global Positioning System tracking device placed on a drug suspect’s car violated his Fourth Amendment rights against unreasonable searches. While the ruling did not directly involve cellphones — many of which also include GPS locators — it raised questions about the standards for cellphone tracking, lawyers say.

The police records show many departments struggling to understand and abide by the legal complexities of cellphone tracking, even as they work to exploit the technology.

In cities in Nevada, North Carolina and other states, police departments have gotten wireless carriers to track cellphone signals back to cell towers as part of nonemergency investigations to identify all the callers using a particular tower, records show.

In California, state prosecutors advised local police departments on ways to get carriers to “clone” a phone and download text messages while it is turned off.

In Ogden, Utah, when the Sheriff’s Department wants information on a cellphone, it leaves it up to the carrier to determine what the sheriff must provide. “Some companies ask that when we have time to do so, we obtain court approval for the tracking request,” the Sheriff’s Department said in a written response to the A.C.L.U.

And in Arizona, even small police departments found cell surveillance so valuable that they acquired their own tracking equipment to avoid the time and expense of having the phone companies carry out the operations for them. The police in the town of Gilbert, for one, spent $244,000 on such equipment.

Cell carriers, staffed with special law enforcement liaison teams, charge police departments from a few hundred dollars for locating a phone to more than $2,200 for a full-scale wiretap of a suspect, records show…

Many departments try to keep cell tracking secret, the documents show, because of possible backlash from the public and legal problems. Although there is no evidence that the police have listened to phone calls without warrants, some defense lawyers have challenged other kinds of evidence gained through warrantless cell tracking.

“Do not mention to the public or the media the use of cellphone technology or equipment used to locate the targeted subject,” the Iowa City Police Department warned officers in one training manual. It should also be kept out of police reports, it advised.

In Nevada, a training manual warned officers that using cell tracing to locate someone without a warrant “IS ONLY AUTHORIZED FOR LIFE-THREATENING EMERGENCIES!!” The practice, it said, had been “misused” in some standard investigations to collect information the police did not have the authority to collect.

“Some cell carriers have been complying with such requests, but they cannot be expected to continue to do so as it is outside the scope of the law,” the advisory said. “Continued misuse by law enforcement agencies will undoubtedly backfire.”