The Obama administration will tell federal judges in New Orleans today that warrantless tracking of the location of Americans' mobile devices is perfectly legal.

Federal prosecutors are planning to argue that they should be able to obtain stored records revealing the minute-by-minute movements of mobile users over a 60-day period -- in this case, T-Mobile and MetroPCS customers -- without having to ask a judge to approve a warrant first.

The case highlights how valuable location data is for police, especially when it's tied to devices that millions of people carry with them almost all the time. Records kept by wireless carriers can hint at or reveal medical treatments, political associations, religious convictions, and even whether someone is cheating on his or her spouse.

"It's at a point now where the public awareness about this specific issue is growing," says Hanni Fakhoury, a staff attorney at the Electronic Frontier Foundation who will be arguing the pro-privacy side before the Fifth Circuit Court of Appeals this morning.

Today's oral arguments are remarkably timely: on Sunday, California Gov. Jerry Brown, a Democrat, vetoed (PDF) a bill that would have required law enforcement to obtain location warrants. And last week, Rep. Zoe Lofgren, a Democrat representing Silicon Valley, introduced pro-warrant federal legislation.

CNET disclosed the Justice Department's warrantless tracking requests in 2005. More than seven years later, the legal landscape remains unsettled, with two other appeals courts taking different approaches, and plenty of lower courts disagreeing. Meanwhile, a coalition of tech companies and advocacy groups including AT&T, Facebook, and Google has been all but begging Congress to update the law to require warrants.

The Justice Department declined to respond to questions from CNET yesterday. James Baker, the associate deputy attorney general, previously told Congress that requiring warrants before police could obtain location data from mobile providers would hinder "the government's ability to obtain important information in investigations of serious crimes."

DOJ: Customers have 'no privacy interest' in cell site records

In a legal brief (PDF) filed before the Fifth Circuit in February, the Justice Department says its position "is consistent with the Fourth Amendment because a customer has no privacy interest in cell-site records, which are business records created and stored by a cell phone provider in its ordinary course of business." It wants location data collected even if the mobile device isn't being used. (The Fourth Amendment prohibits "unreasonable" searches and seizures.)

Lending a boost to arguments made by the EFF and the ACLU -- and, in separate briefs, the Electronic Privacy Information Center and law professor Susan Freiwald -- is a recent ruling by the U.S. Supreme Court on GPS tracking. The January opinion, written by Justice Antonin Scalia, said that the customary law enforcement practice of installing physical GPS bugs on a car for 28 days was a "physical intrusion" and trespass that triggered the Fourth Amendment.

U.S. Department of Justice

Scalia suggested that non-physical surveillance might also raise constitutional concerns: "It may be that achieving the same result through electronic means, without an accompanying trespass, is an unconstitutional invasion of privacy, but the present case does not require us to answer that question." Five other justices, however, suggested they had constitutional concerns with long-term tracking.

"If tracking a vehicle over 28 days violates a reasonable expectation of privacy, then tracking a cell phone for more than twice that period surely violates such an expectation as well," the civil liberties groups told the Fifth Circuit. "The warrant and probable cause requirements are essential to ensuring that these invasive searches do not take place without adequate justification."

The Justice Department's position is straightforward: a wireless customer "has no reasonable expectation of privacy" in location data, in part because he or she has "voluntarily conveyed" that information to a wireless provider. "Obtaining historical cell-site information is not invasive or intrusive" and this is a "routine" investigation, its brief (PDF) says.

Prosecutors say all that's necessary is what's known as a 2703(d) order, which requires law enforcement to demonstrate that the records are "relevant and material to an ongoing criminal investigation." Because that standard is easier to meet than that of a search warrant based on probable cause, it's less privacy-protective.

An October 2010 opinion by U.S. Magistrate Judge Stephen Smith in Texas rejected prosecutors' requests for a (d) order, saying they were seeking "continuous location data to track the target phone over a two month period, whether the phone was in active use or not."

Prosecutors had requested any information regarding "the antenna tower and sector to which the cell phone sends its signal," which can yield a location fix down to as a little as a few hundred feet, depending on the tower placement and the technology used. (They did, however, appear not to request handset-based GPS data, which is more precise.)

No matter what the outcome of today's arguments before the Fifth Circuit, the losing side is nearly certain to appeal. Predicts Fakhoury, the EFF attorney: "That's exactly the type of situation the Supreme Court is going to get involved in."