We’ve seen the movies and the TV shows. We know how the FBI finds people. In addition to old-fashioned gumshoe sleuthing, it plies a handful of high-tech tricks. It tracks ATM usage and credit-card swipes. And these days, it can get information from cell-phone companies to figure out precisely where calls are coming from.

But how easy should it be for the FBI or other law enforcement authorities to pull cell-phone data showing a user’s location? Is it enough for authorities to show that it has “reasonable grounds” to believe that the data is “relevant and material to an ongoing investigation?” Or should a higher standard apply? Should a law enforcement have to have “probable cause,” as established by the Fourth Amendment?

The issue is all teed up for argument Friday at the Third Circuit in Philadelphia. Click here for a preview from Proskauer’s Jeff Neuberger, who’s not involved in the case; click here for an op-ed in Thursday’s Philadelphia Inquirer; here for a piece on the case from Newsweek, which has links to filings in the case.

The quick backstory: In late 2007, the United States applied for court permission to obtain information about the location of an individual’s cell phone, without showing probable cause that tracking the individual would turn up evidence of a crime. A magistrate judge denied the government’s request and a district court upheld that decision in September 2008. The government is appealing the ruling in the U.S. Court of Appeals for the Third Circuit. According to Newsweek, the hearing will represent the first time a federal appellate court has hear arguments on the legality of the data-collecting methods.

The Electronic Frontier Foundation, along with the ACLU, are arguing that the Third Circuit should uphold a lower court’s ruling that the higher standard should apply.

Wrote the ACLU’s Catherine Crump, in her Inquirer op-ed:
What’s at stake in the case is not whether it’s OK for the government to track the locations of cell phones; we agree that cell-phone tracking is lawful and appropriate in certain situations. The question is whether the government should first have to show that it has good reason to think such tracking will turn up evidence of a crime.

We believe it should. This case is not about protecting criminals. It’s about protecting innocent people from unjustified violations of their privacy.

The government is arguing that the lower standard should apply. According to Newsweek’s writeup, the DOJ contends that many of the concerns about their practices are “outlandish” and overblown. The government argues that cell-phone tracking records are “routine business records” that contain “non content” data and are therefore “unprotected” under the Fourth Amendment of the Constitution.

So how are folks supposed to avoid the government tracking data about them? Wrote the prosecutors, in their brief: “One who does not wish to disclose his movements to the government need not use a cellular telephone.”