Digital Bread Crumbs: Following Your Cell Phone Trail If you use a mobile phone, you're leaving a record of where you've been. But where does your phone say you are? If it relies on cell phone towers for that information, your location may be vague. GPS-enabled phones are more specific. The difference between the two can be miles wide.

Digital Bread Crumbs: Following Your Cell Phone Trail

Digital Bread Crumbs: Following Your Cell Phone Trail

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Third in a four-part series

Jeff Fischbach is a little bit like those guys in The Matrix — when he puts on his shades and looks at the world, he sees data.

Walking down the street in San Francisco, he points out all the devices that record people's comings and goings: digital parking meters, apartment intercom systems, digital security cameras.

"Anything with a computer is going to keep a log," Fischbach says.

Fischbach is a forensic technologist. Lawyers eagerly pay for his ability to extract evidence from everyday devices — he's even checked alibis on kitchen appliances. But when it comes to tracking where people go, he says, the most common source of data is in your pocket.

"Cell phones leave a data trail," he says. "And it's becoming standard for major police departments and the feds to use this data." (Story continues after the gallery.)

Finding Your Location

Fischbach says he has worked on at least 250 criminal cases that relied on cell phone data. It's almost unusual to find prosecutors who don't check cell phone records, he says.

"More and more I'm finding that it's being used as the sole evidence in a case," Fischbach says. "That concerns me a little bit."

Fischbach will work for the prosecution or the defense.

At a meeting with Robert Amparan, a San Francisco lawyer defending a young man charged with a gang-related homicide, Fischbach helps to make sense of a sheaf of printouts from a local cell phone company. It is data from the cell phone towers that prosecutors are using to place the defendant at the scene of the shooting.

Following the Sept. 11 attacks, President Bush signs the USA Patriot Act into law. Doug MIlls/AP hide caption

Timeline: Key Moments In The History Of Privacy In The U.S.
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Doug MIlls/AP

Fischbach is here to translate the codes and to provide the defense with some reasonable doubt.

"They can't say he was here," Fischbach tells the lawyer. "What they can say is he could have been at the crime scene. That cell sector covers the crime scene."

The location is vague because this phone relies only on tower data — that is, the records of which cell tower the defendant's phone was connecting through and from which angle. Depending on the density of the tower network, the margin of error can be as much as a couple of miles.

But that margin is shrinking.

Newer phones come with optional GPS, the satellite-based location service, which users can choose to turn on, though at a considerable cost to battery life.

Even with the GPS off, phone location is getting more precise. Some phones use more than one tower to triangulate their locations. Others "find" themselves by locating nearby Wi-Fi signals and checking them against a master catalog of Wi-Fi signals with known coordinates.

While location data aren't enough to prove guilt or innocence, they can be very useful to investigators. Police can find potential witnesses. Employers can double-check mileage claims on an expense report.

Looking At Your Location

So the big question is, who gets to see these records?

Fischbach says, "It's really all over the map."

When it comes to requests for tower data, he says, some cell companies just require subpoenas. Others require warrants, which presuppose a probable cause and the involvement of the court.

Sometimes, Fischbach says, all it takes is a little charm.

""I even managed to get that sort of information for a defendant recently just by calling up and speaking to someone who was pretty friendly," he says.

Real-time tracking requires a warrant — the courts have settled that — but there's a lot less certainty about the privacy of the records of where a cell phone has been.

Jennifer Granick, the civil liberties director at the Electronic Frontier Foundation, calls the situation a "mess." The federal law covering cell phone location records is out of date and overly complex, Granick says.

"Normal people can't understand it, defense attorneys can't understand it, a lot of judges can't understand it, and really, when you drill down, it doesn't make a lot of sense," she says.

Federal law puts a lot of importance on esoteric, technical details. For instance, the privacy of the records often depends on which technology was used to calculate the phone's location.

"It doesn't seem, I think, to the average cell phone owner that there should be a big difference," Granick says. "But because of the technological way that people can get access to your location information, the law, surprisingly, treats them very differently."

And this leads to uncertainty for law enforcement, too.

Expectation Of Privacy?

In theory, detectives could get a quick list of potential witnesses by requesting the numbers of all the phones using a certain tower at a given time. But few departments take advantage of this tool. That's because it sometimes takes too much effort to sift through that many names and numbers.

But it's also because courts haven't settled whether that kind of digital dragnet is acceptable. Oklahoma County, Okla., First Assistant District Attorney Scott Rowland is one prosecutor who says it is. Rowland says people in public places don't have any more expectation of privacy for their phone location than they do for their car's presence at the shopping mall.

"Police can go up and down the row and take tag numbers and run them to see who's at the mall," Rowland says. "You don't have an expectation that others won't see you there."

Rowland gives seminars to fellow prosecutors on how to use phone data. He tells them they don't need a warrant for tower data, but he says they should probably get one, anyway, because the law is still so unsettled.

"It's a little surprising to me that the federal courts have been in my opinion a little bit slow to take on one of these head-on and resolve the issue," Rowland says.

There is a case pending in the 3rd U.S. Circuit Court of Appeals that some experts believe will help define the privacy protections for cell tower location records.

Finding Your Friends On A Map

Meanwhile, phone location is becoming an ever more visible part of everyday life.

"A person's location is a great conversation starter," says Steve Lee, the product manager for Google Latitude. It's one of several competing services that allow people to share their location with friends.

Steve Lee of Google Latitude, which allows mobile phone users to share their location with friends. Google is considering whether to experiment with ads that target phones based on their location. Martin Kaste/NPR hide caption

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Martin Kaste/NPR

Steve Lee of Google Latitude, which allows mobile phone users to share their location with friends. Google is considering whether to experiment with ads that target phones based on their location.

Martin Kaste/NPR

Lee says phone location services are a social tool, good for finding friends in a crowd, or colleagues at a conference. The service is free; Lee says Google hopes to make money from an increase in Web searches by people using the location service on their smart phones.

Lee says the company may also experiment with ads tailored to a phone's location.

Right now, Google is going slowly, limiting what the tracking software can do. For instance, Latitude does not keep a record of where users have been, even though Lee says that data would be "very valuable."

Lee says phone location tracking is something that strikes some people as "cool but creepy."

"Over time, people will become more and more comfortable with it," he says. "But not everyone's going to be comfortable with this, and they don't need to share their location with other people."

Fischbach, the forensic technologist, is in the "cool but creepy" camp. He's creeped out by what his own phone can do.

"I walked around my own house, and it's not a mansion, and I could see on the phone where I was standing in the house," he says, adding that he usually keeps the GPS option switched off.

At the same time, Fischbach welcomes the arrival of services like Google Latitude and a similar platform called Loopt. He says all they're really doing is making visible the kind of data that he sifts through for a living. And he says it's probably good that people start seeing the trail of digital bread crumbs that they've been leaving all along.