A woman holding a cellphone descends down an escalator at the Pentagon Metro Station in Arlington, Va. on July 8. (Marlon Correa/The Washington Post)

The Justice Department announced a policy Thursday that will require its law enforcement agencies to obtain a warrant to deploy cellphone-tracking devices in criminal investigations and inform judges when they plan to use them.

The new policy, announced by Deputy Attorney General Sally Quillian Yates, should increase transparency around the use of the controversial technology by the FBI and other Justice Department agencies. It imposes the highest legal standard for the device’s use and a uniform standard across the department.

The policy change is an acknowledgment by the Justice ­Department that the use of the devices — sometimes called StingRays, the name of one popular model — raises serious privacy concerns.

But the policy does not apply to state and local agencies, which continue to use the tracking technology, often without expressly informing a judge and obtaining a warrant based on probable cause. And some lawmakers have raised concerns about whether exceptions to the warrant requirement are too broad.

The new policy, Yates said in a briefing with reporters, was designed “to promote transparency and consistency and accountability, all while being mindful of the public’s privacy interest.”

The devices are boxes about the size of a small suitcase that can help investigators locate suspects by identifying signals coming from their cellphones. But the machines, which simulate cell towers, also sweep up data from innocent bystanders in the suspect’s vicinity.

The data captured by the devices are serial numbers from cellphones, not GPS coordinates. The technology used by federal authorities does not capture ­e-mails, texts, contact lists, images or any other data from the phone, officials said.

Such devices have also been deployed on planes flown by the U.S. Marshals Service in pursuit of criminal suspects. Other federal agencies that have purchased the equipment include the Drug Enforcement Administration, Immigration and Customs Enforcement, and the Bureau of Alcohol, Tobacco, Firearms and Explosives.

The Justice Department policy does not apply to other departments or overseas investigations by the FBI and other agencies.

“The Department of Justice’s new policies are finally starting to catch up with the rapid advancement of this tracking technology,” said Sen. Patrick J. Leahy (Vt.), ranking Democrat on the Judiciary Committee. But he said that he has “serious questions” about the exceptions to the warrant requirement and that he will press the department to justify them.

The new policy waives the warrant requirement for exigent circumstances. These include the need to protect human life “or avert serious injury,” prevent the imminent destruction of evidence, the hot pursuit of a fleeing felon, or the prevention of escape by a convicted fugitive from justice.

The technology, which is powerful enough to penetrate the walls of homes, was developed for use by intelligence agencies and has since been adopted by law enforcement. At least 53 state and local law enforcement agencies in 21 states and the District of Columbia have bought such devices.

Under the new policy, data gathered by authorities must be deleted as soon as the suspect’s phone is located, or if they fail to locate it, all data gathered must be deleted at least once a day. In cases in which officials know where a suspect is but do not know his or her phone number, they may set up a simulator nearby to try to identify through patterns over time the suspect’s phone. In those cases, the data gathered must be disposed of either when they’ve located the phone or at least once every 30 days.

Authorities must also keep data that could help prove a suspect’s innocence.

“This is a really positive development that makes important strides towards protecting the privacy rights of Americans,” said Nathan Wessler, a staff attorney with the American Civil Liberties Union. “It leaves some questions unanswered, but it is a strong improvement over the patchwork of less protective policies we saw before.”

The department’s policy resulted from a review of existing practice in the wake of a number of high-profile news stories focusing on the concerns of privacy advocates and judges, who often were unaware the devices were being used. The policy now also requires that in applying to a court for a warrant, prosecutors and law enforcement officers must disclose the planned use of the tracking technology and how it will be used.

In some cases, after consulting with federal authorities, state and local prosecutors have settled criminal cases rather than proceed with prosecutions that could reveal to defendants details about the use of the devices.

The policy’s warrant requirement tracks with the FBI’s, which as of April required a search warrant before agents could use a cellphone tracker. Prior to the change, officials said, some Justice Department agencies sought a court order based merely on an assertion that the data sought was relevant to a criminal investigation. Often, the order was used to obtain cell-tower data from a phone company — a preliminary step before using a StingRay, and the judge often was not told that the cell-site simulator was going to be used.

The policy also requires annual reporting by each division or district office to its agency headquarters reflecting the number of times a cell-tower simulator is used; the number of uses at the request of other agencies, including state or local law enforcement; and the number of uses in emergencies.