AUDIE CORNISH, HOST:

Cessna airplanes may be spying on us by picking up data from our cell phones. According to a report in today's Wall Street Journal, the U.S. government has been using the technology in this broader way for several years now. The reporter who broke this story is Devlin Barrett. He joins us from the Journal's offices in Washington. Welcome to the program, Devlin.

DEVLIN BARRETT: Hi, Audie.

CORNISH: So, break it down for us. Which agency is utilizing this technology and what exactly is it that they're doing?

BARRETT: Well, it's used by the U.S. Marshals Service, and one of their main tasks is to hunt fugitives, and they're pretty good at it. And they use this technology, essentially, to scan the sea of digital breadcrumbs in the air to find the specific cell phone of a suspect they're looking for. Now, in the course of doing that - because this is essentially, a flying, fake cell phone tower - it's in a plane flying over, you know, either a city or a county or wherever they think the target might be - it can scoop up tens of thousands of people's identification information from their phones in the course of a single flight.

CORNISH: So you're saying, when you call it a fake cell phone tower, it's basically tricking the phones into sending information to it?

BARRETT: That's right. Because every cell phone is built to talk to the closest, strongest signal, right? And this device tricks every cell phone that can hear it into thinking that that device is the closest signal.

CORNISH: So a scenario could be, in an investigation where they send one of these planes over a city block looking for the phone of one particular fugitive. The question is, what do they do with the rest of information, right? Like, if I'm in my apartment on that same city block, what happens to my data?

BARRETT: Well, your registration identification number gets sent up into the machine. The machine checks it against the number it's looking for, decides that's not what it's looking for and, in the non-technical parlance of the machine, it lets go of your phone. And the concern from a lot of the privacy advocates is what happens with that data after you've done that process, because we know that, when it's used in a foreign-spy military setting, which the U.S. Government does, they do maintain that data and they do build databases. What we're told today is - the Justice Department official says they do not maintain a database of U.S. user's cell phones. So the unanswered question so far is are the machines themselves holding onto some of this data?

CORNISH: This technology has been around for a while, right? It's been used in police cars to scan a limited area for phone signals. What's remarkable about the way the marshals are using it domestically?

BARRETT: Well, what this is is really a major evolution of the technology. We've known about a device called the Stingray which is, like you said, used in cars and used to, sort of, scan a street, basically. This is, essentially, a Stingray on steroids. A Stingray - maybe it picks up a few hundred cell signals from different phones. These devices are built so that if you're in a crowded area, you can pick up tens of thousands. And, as one privacy advocate said to me - how may people's privacy rights is it worth intruding on to find one suspect? Is a hundred enough, but 10,000 too much? What about a hundred-thousand, if you do it over and over? Is there a point at which you are scanning too many people's phones for it to be OK?

CORNISH: The Justice Department also maintains, quote, "in deploying any such equipment or tactics, federal law enforcement agencies comply with federal law, including seeking court approval." Is that clear to you in your reporting?

BARRETT: Yes. It's clear. But what's really unclear about it, because we can't see the court orders because they're sealed, is what do the judges know that they're signing off on when they sign off on it? It's just not clear if the court system knows that it's approving this particular method when it approves these searches.

CORNISH: Devlin Barrett, with all of the revelations in the last few years about the NSA domestic spy surveillance program, it's very tempting to hear this and assume that this is linked in some way. And the Justice Department has said, quote, that "it would be utterly false to conflate this program with the collection of bulk phone records by the national security agency." What is the difference to you?

BARRETT: Well, the difference is the database, right? The U.S. government has said now that they do not create a database. We know they have the capability. We're told they don't use it. I think with a lot of these surveillance issues, it really depends on whether you trust the government or not to do the right thing and to do it carefully. And, so I think if you don't, then this probably worries you. I think if you do trust the government to do the right thing and do it carefully, you probably think this is a good thing and a worthwhile thing to be doing.

CORNISH: Devlin Barrett. He's from The Wall Street Journal. Devlin, thanks so much.

BARRETT: Thank you, Audie. Transcript provided by NPR, Copyright NPR.