BOB GARFIELD:

This week the Supreme Court decided a case called U.S. vs. Jones, which may have raised more questions than it answered. In that case, the Washington DC police affixed a GPS device to the car of suspected drug dealer Antoine Jones for 28 days and amassed enough evidence to earn him life in prison. The Supreme Court ruled that tracking Jones violated his Fourth Amendment rights against unreasonable search and seizure.

The case set a precedent that merely attaching a GPS device to a car with the intent to collect data constitutes a search. But the Court explicitly did not rule on whether that type of search is categorically unreasonable under the Fourth Amendment.

Confused? Orin Kerr, law professor at George Washington University and blogger for The Volokh Conspiracy, says that by not deciding whether attaching a GPS device is unreasonable, the Court left law enforcement with too little to work with.

ORIN KERR:

We know one thing with certainty, that the government can't place a GPS device on a car with no reason to think that there is any criminal conduct afoot. And that applies to the federal government and it applies to the state government.

What we just don't know is if the government needs to get a search warrant, we don't know if the government needs just probable cause without a warrant. We don't know how much the government needs to do before installing a GPS device, but we know that they can't just install it on anyone's car without any cause at all.

BOB GARFIELD:

I'm interested though in the D.C. Circuit Court decision that led up to the Supreme Court case. The prosecution argued that the threshold of search doesn't necessarily happen the first moment a GPS is put on the car, that it has to be on there for a certain period of time before it rises to the level of search. Can you tell me about the mosaic theory?

ORIN KERR:

The idea is instead of looking at whether an individual act is unconstitutional maybe you should look at whether acts over a period of time are sort of collectively unconstitutional. And that would allow the government to install a GPS device for a limited period of time and then maybe require a warrant when the GPS device has been used for more than a week or two weeks; we don't exactly know where the dividing line is.

Although the majority in the Supreme Court did not embrace this theory, a few justices wrote additional opinions in which they indicated they very well might be willing to accept it in a future case.

BOB GARFIELD:

How in the world would any law enforcement agency be able to interpret when this threshold has been reached to constitute unreasonable search? And how in the world could a court itself determine when that threshold has been passed? It is so subjective.

ORIN KERR:

The problem with the mosaic theory is nobody knows if 10 days of monitoring is too much or 20 days. The concurring opinion by Justice Alito in the Jones case said we don't know exactly where the line is but 30 days, which is the amount of monitoring in the Jones case, was too much.

I tend to think if the Supreme Court in a future case has to grapple with this issue, they won't want to adopt this mosaic theory because of these difficult line-drawing problems. But that's just a prediction, and we're gonna have to wait and see.

BOB GARFIELD:

Can those of us who worry about police intrusion take heart in the fact that the justices ruled that GPS is, in fact, a search?

ORIN KERR:

If you're worried about privacy, if you're worried about how new technologies threaten privacy, this is a terrific decision. There's not a lot of clarity but there are strong suggestions that the Court would be willing to adopt new privacy protections that we have not yet seen before. And more generally, nine justices of the Supreme Court are worried about privacy, just like a lot of Americans are.

BOB GARFIELD:

And, on the flip side, if you're worried about putting bad guys in jail using reasonable police tools for so doing, should you be alarmed?

ORIN KERR:

The Supreme Court over US history has tried to tailor the constitutional protections to new technologies. The Supreme Court justices try to adjust the level of constitutional protection to try to restore the traditional balance of the Constitution. At least so far, we see the nine justices very much engaged in the problem.

BOB GARFIELD:

Now, as I understand it, it actually expands the definition of privacy under the Fourth Amendment. Can you tell me more?

ORIN KERR:

For the last 40 years or so, the Supreme Court has said that the Constitution only protects reasonable expectations of privacy. In the Jones case, the Court said the Constitution does protect reasonable expectations of privacy, but it also protects against government conduct that was a trespass as of the time of the framing of the Constitution.

BOB GARFIELD:

So 220 years ago, when GPS technology was at a very early stage, what — [LAUGHS] —

[KERR LAUGHS]

- what constituted trespass?

ORIN KERR:

There is some disagreement in the opinions in the Jones case as to what was trespassed at the time, but the idea is touching somebody else's property with an intent to find something out by doing that.

So what the Court said was when the GPS device was installed that itself was not a constitutional search but installing the GPS device with an intent to get information from the GPS device, that was a trespass.

BOB GARFIELD:

So a cop putting a GPS tracker on your car is trespass, provided he does so with the intention of keeping track of you. But if he just does it as a decorative element, the Court's down with that.

ORIN KERR:

Strange, but true. The Court [LAUGHS], in fact, comes out and says, if it's just installing the device without any intent to ever use it, that's okay; that's not a constitutional search.

BOB GARFIELD:

Orin thank you so much.

ORIN KERR:

Thank you for having me.

BOB GARFIELD:

Orin Kerr is a professor of law at George Washington University and contributor to the blog The Volokh Conspiracy.