Mobile phones interact with cell towers constantly, sending and receiving location information in some instances without input from the user. For law enforcement, tower data can prove a powerful investigative tool — potentially linking a person to suspected criminal activity.

But how easily should the authorities be able to obtain information from a phone company about a person’s movement? Should investigators have to meet the probable-cause standard and obtain a warrant? There is no consensus.

Increasingly, judges across the country are confronting — and dividing over — new and challenging legal issues under the Fourth Amendment that pit emerging technology and law enforcement demands against a person’s privacy expectations.

"Cell-tower information reveals a great deal of detail about a particular person," said Hanni Fakhoury, a staff attorney with the digital-rights group Electronic Frontier Foundation in San Francisco. "Requiring a search warrant has traditionally been the balance struck between allowing the police to get access to this information and protecting privacy."

The foundation and the Washington-based Center for Democracy & Technology are backing a man named Antoine Jones in a pending fight over cell-tower data in U.S. District Court for the District of Columbia.

Jones was at the center of the landmark U.S. Supreme Court ruling in January in which the court concluded that the warrantless installation and monitoring of a GPS device to track Jones violated his privacy rights. The high court upheld the reversal of his conviction and life sentence for his alleged role in a drug-trafficking conspiracy.

Jones’ lawyer, A. Eduardo Balarezo, a solo practitioner in Washington, is now trying to convince a trial judge to suppress the tower data that prosecutors intend to use against Jones at a new trial. In the earlier proceedings, DOJ lawyers successfully used GPS data — from a device covertly attached to Jones’ vehicle — to connect him to a drug stash house in Maryland. "In this case, the government seeks to do with cell site data what it cannot do with the suppressed GPS data," Balarezo said in court papers.

Prosecutors haven’t yet responded to Jones’ effort to void the cell-tower information, which agents obtained through a court order that didn’t involve a showing of probable cause.

In a case pending in the U.S. Court of Appeals for the Fifth Circuit, DOJ lawyers contend historical cell-site information is a business record — held by a third party — that does not implicate privacy rights. In that case, set for argument October 2, a magistrate judge, Stephen Smith of U.S. District Court for the Southern District of Texas, denied three DOJ applications to obtain cell-site records, saying the warrantless disclosure of cell-site data violates the Fourth Amendment. DOJ lawyers, including Nathan Judish in the agency’s Computer Crime and Intellectual Property Section, are appealing the decision. Judish declined to comment.

THIRD-PARTY DOCTRINE

Jones, the owner of a nightclub in Washington, was the target of a joint FBI and Washington police narcotics investigation in 2004. With the aid of the GPS device, prosecutors tied Jones to a house that yielded thousands of dollars in cash and a substantial amount of cocaine. Jones was convicted at trial in 2008 on a conspiracy charge and sentenced to life behind bars.

The U.S. Court of Appeals for the D.C. Circuit two years ago struck Jones’ conviction, finding the warrantless use of a GPS tracking device a violation of the Fourth Amendment. With the closely watched case back in Washington’s federal trial court, the dispute now centers on whether prosecutors should be allowed to use cell-tower data.

On August 13, the Electronic Frontier Foundation legal team filed an amicus brief supporting Jones’ fight to suppress the cell-site information the authorities collected over a six-month period.

A primary question in the case centers around whether a person has any control over the data that a mobile phone transmits to a tower. Privacy advocates argue that mobile phone users do not voluntarily turn over location information to a third-party phone company.

"Users do not enter their location into the phone the way they dial the number of the party they are calling," the electronic rights group said in the brief. "They do not take any affirmative action to create location information at all. In fact, their location is generated automatically, often without their intent, knowledge or control."

DOJ lawyers contend that cell-site records are not nearly as precise as GPS data and that a lower standard therefore should be in place to acquire tower information. The probable-cause threshold, DOJ argues, should be reserved for intrusive investigative techniques that include wiretaps and search warrants.

Justice Sonia Sotomayor in the Supreme Court’s decision in the Jones case had her eye on the so-called "third-party doctrine" and its interaction with privacy rights. But the court didn’t go so far as to rule on cell tracking.

"It may be necessary to reconsider the premise that an individual has no reasonable expectation of privacy in information voluntarily disclosed to third parties," Sotomayor wrote. "This approach is ill suited to the digital age, in which people reveal a great deal of information about themselves to third parties in the course of carrying out mundane tasks."

George Washington University Law School professor Orin Kerr, who has written about surveillance and technology, called cell-site location data "the next battleground" over the scope of Fourth Amendment protection. "It’s a clash between old Supreme Court law and what the court might in the future do," he said.

Mike Scarcella can be contacted at mscarcella@alm.com.