The U.S. Supreme Court on Wednesday will hear arguments on the limits of privacy in an age where we all carry around devices capable of tracking our location.

In Carpenter v. U.S., the central question before the court is whether authorities should have had to get a warrant for several months' worth of a suspect's cell-site location information or if his privacy interests under the Fourth Amendment were given up under the “third-party doctrine.”

Arguing against the government is ACLU staff attorney Nathan Wessler. In an interview on Law.com's “Unprecedented” podcast, Wessler explained why he doesn't think the third-party doctrine applies to today's technology. Below is an excerpt from the conversation.

Listen to the full podcast online here or on your iOS or Android device. This excerpt has been edited for clarity and length.

Want more coverage from the intersection of technology and the law? Click here to sign up for Ben Hancock's weekly briefing, What's Next—a look at the courtroom clashes and policy choices that loom over emerging technologies.

“Unprecedented” host Ben Hancock: You equate the data that authorities can get through cell sites as almost like a GPS. The government says it's more approximate—somewhere between a half-mile and 2 miles. Talk to me about the technology of the cell site.

Nathan Wessler: The records from Mr. Carpenter's case are from 2010 and 2011, and the government's right that in those records most of the individual location points are less precise than GPS coordinates. But they still are highly revealing and still, we think, really infringe on people's expectation of privacy. … When we took a look at the records ourselves, we were able to tell things like when he slept at home and when he slept at a neighborhood four miles away in Detroit. We were able to look at his pattern of movements every Sunday afternoon, when in fact he was going to church. So quite sensitive.

But in the intervening seven years that it's taken for this case to make its way up to the Supreme Court, the technology has really changed in significant ways so that location points are more and more precise every year. As more people are using smartphones and using more data on them, carriers have had to erect more cell towers to handle that large amount of data bandwidth. And that means towers get closer together, so their coverage area shrinks, which means you can more precisely locate someone.

Carriers are also deploying hundreds of thousands of what are called “small cells,” which are kind of like little mini cell towers that cover smaller areas. If a customer of a service provider has poor reception in their house, they might be able to install one of these right in their home.

Hancock: Professor Orin Kerr of George Washington University has had a lot to say about the third-party doctrine, and he argues that using the cell network is the modern-day equivalent of walking out into public space to deliver a message. I take it you disagree with that, but tell me why that's wrong.

Wessler: I think the important point isn't that I disagree with that—which I do—but it's that five members of the Supreme Court have already said that they disagree with that. That's the five justices who concurred in the Jones opinion. The government's argument in Jones, about GPS tracking, was to rely on a case from the 1980s, United States v. Knotts, where police used a rudimentary beeper tracking device that they had surreptitiously put in a canister … and the court in the 1980s said, “Look, this is just a half-step beyond normal visual surveillance where you're tailing a suspect for a short period of time. No warrant is required.”

But in Jones, now in the digital age talking about a very powerful GPS device that can track someone without any involvement of police for weeks on end and just send the information to a police computer somewhere, the court said that old rule just doesn't apply anymore. There's something qualitatively different between the kind of effortful action of having to follow a car with a radio receiver, and if you lose the car they had to send in a helicopter to find it again. That's just not the same as this kind of cheap, easy, and invasive electronic tracking.

Sure, if I walk outside, I fully expect that there may be some number of people who happen to see me when I go to the mailbox, or [when] I go to a store or a restaurant, or I get in my car. But what we've never expected—and this is what the five justices explained in Jones—is that there would be someone following us, hour after hour for days and weeks and months, without blinking, without taking a bathroom break, without taking a nap. That kind of pervasive surveillance just violates our expectations of privacy and is regulated by the Fourth Amendment.

Hancock: This order for the cellphone location records was issued under the Stored Communications Act, I think Section 2703. Do you see that there's an inherent conflict between this provision of the SCA and the Fourth Amendment, such that the provision itself is unconstitutional, or is it purely a matter of interpreting the SCA in the right way?

Wessler: The short answer is that Congress actually has a kind of safety valve provision in the Stored Communications Act that provides a way to get a warrant for these kinds of records. The background is that Congress passed the [SCA] in 1986. A fraction of 1 percent of all Americans had cellphones in 1986; there were about 1,000 cell towers in the whole country compared to more than 300,000 today. … They amended the statute in 1994 to include the current language to allow for that court order provision; about 9 percent of Americans had cellphones in 1994, there were about 18,000 cell towers. So, again, just a fraction of the coverage here. And there's no indication in the legislative history at all that Congress was thinking about the existence of these location records or the fact that the government might want to get someone's historical location from their cellphone service provider.

And so Congress wasn't thinking about this in particular. But Congress did create two options—two mechanisms—for police to go to a company to get telecommunications service records. Either an order under section 2703(d), the kind of order they got here, or a search warrant. And the only logical reason they did that is that Congress realized there might be some kinds of records they hadn't thought about yet that would be very private and that might be regulated under the Fourth Amendment, and so they should create a mechanism for getting those without violating the Constitution.

The U.S. Supreme Court on Wednesday will hear arguments on the limits of privacy in an age where we all carry around devices capable of tracking our location.

In Carpenter v. U.S., the central question before the court is whether authorities should have had to get a warrant for several months' worth of a suspect's cell-site location information or if his privacy interests under the Fourth Amendment were given up under the “third-party doctrine.”

Arguing against the government is ACLU staff attorney Nathan Wessler. In an interview on Law.com's “Unprecedented” podcast, Wessler explained why he doesn't think the third-party doctrine applies to today's technology. Below is an excerpt from the conversation.

Listen to the full podcast online here or on your iOS or Android device. This excerpt has been edited for clarity and length.

Want more coverage from the intersection of technology and the law? Click here to sign up for Ben Hancock's weekly briefing, What's Next—a look at the courtroom clashes and policy choices that loom over emerging technologies.

“Unprecedented” host Ben Hancock: You equate the data that authorities can get through cell sites as almost like a GPS. The government says it's more approximate—somewhere between a half-mile and 2 miles. Talk to me about the technology of the cell site.

Nathan Wessler: The records from Mr. Carpenter's case are from 2010 and 2011, and the government's right that in those records most of the individual location points are less precise than GPS coordinates. But they still are highly revealing and still, we think, really infringe on people's expectation of privacy. … When we took a look at the records ourselves, we were able to tell things like when he slept at home and when he slept at a neighborhood four miles away in Detroit. We were able to look at his pattern of movements every Sunday afternoon, when in fact he was going to church. So quite sensitive.

But in the intervening seven years that it's taken for this case to make its way up to the Supreme Court, the technology has really changed in significant ways so that location points are more and more precise every year. As more people are using smartphones and using more data on them, carriers have had to erect more cell towers to handle that large amount of data bandwidth. And that means towers get closer together, so their coverage area shrinks, which means you can more precisely locate someone.

Carriers are also deploying hundreds of thousands of what are called “small cells,” which are kind of like little mini cell towers that cover smaller areas. If a customer of a service provider has poor reception in their house, they might be able to install one of these right in their home.

Hancock: Professor Orin Kerr of George Washington University has had a lot to say about the third-party doctrine, and he argues that using the cell network is the modern-day equivalent of walking out into public space to deliver a message. I take it you disagree with that, but tell me why that's wrong.

Wessler: I think the important point isn't that I disagree with that—which I do—but it's that five members of the Supreme Court have already said that they disagree with that. That's the five justices who concurred in the Jones opinion. The government's argument in Jones, about GPS tracking, was to rely on a case from the 1980s, United States v. Knotts, where police used a rudimentary beeper tracking device that they had surreptitiously put in a canister … and the court in the 1980s said, “Look, this is just a half-step beyond normal visual surveillance where you're tailing a suspect for a short period of time. No warrant is required.”

But in Jones, now in the digital age talking about a very powerful GPS device that can track someone without any involvement of police for weeks on end and just send the information to a police computer somewhere, the court said that old rule just doesn't apply anymore. There's something qualitatively different between the kind of effortful action of having to follow a car with a radio receiver, and if you lose the car they had to send in a helicopter to find it again. That's just not the same as this kind of cheap, easy, and invasive electronic tracking.

Sure, if I walk outside, I fully expect that there may be some number of people who happen to see me when I go to the mailbox, or [when] I go to a store or a restaurant, or I get in my car. But what we've never expected—and this is what the five justices explained in Jones—is that there would be someone following us, hour after hour for days and weeks and months, without blinking, without taking a bathroom break, without taking a nap. That kind of pervasive surveillance just violates our expectations of privacy and is regulated by the Fourth Amendment.

Hancock: This order for the cellphone location records was issued under the Stored Communications Act, I think Section 2703. Do you see that there's an inherent conflict between this provision of the SCA and the Fourth Amendment, such that the provision itself is unconstitutional, or is it purely a matter of interpreting the SCA in the right way?

Wessler: The short answer is that Congress actually has a kind of safety valve provision in the Stored Communications Act that provides a way to get a warrant for these kinds of records. The background is that Congress passed the [SCA] in 1986. A fraction of 1 percent of all Americans had cellphones in 1986; there were about 1,000 cell towers in the whole country compared to more than 300,000 today. … They amended the statute in 1994 to include the current language to allow for that court order provision; about 9 percent of Americans had cellphones in 1994, there were about 18,000 cell towers. So, again, just a fraction of the coverage here. And there's no indication in the legislative history at all that Congress was thinking about the existence of these location records or the fact that the government might want to get someone's historical location from their cellphone service provider.

And so Congress wasn't thinking about this in particular. But Congress did create two options—two mechanisms—for police to go to a company to get telecommunications service records. Either an order under section 2703(d), the kind of order they got here, or a search warrant. And the only logical reason they did that is that Congress realized there might be some kinds of records they hadn't thought about yet that would be very private and that might be regulated under the Fourth Amendment, and so they should create a mechanism for getting those without violating the Constitution.