DAVID GREENE, HOST:
We now know that, for years, the National Security Agency has been collecting the records of Americans' phone traffic. The government insists these are just billing records, who called whom, not the content of the calls.
Administration officials, like Deputy Attorney General James Cole, maintain that unlike the content of calls, these records do not require a search warrant.
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GREENE: Well, why aren't they?
NPR's Larry Abramson reports on the court case behind that statement, and why some people think it is time to review it.
LARRY ABRAMSON, BYLINE: On March 5th, 1976, in Baltimore, Maryland, Patricia McDonough was robbed. That's the opening line of the Supreme Court ruling in Smith v. Maryland, a case that forms one of the building blocks of modern privacy law.
George Washington University law professor Orin Kerr picks up the story of how police investigated that robbery.
ORIN KERR: They got some leads to see that the robber might be Michael Smith, whose car was parked outside of McDonough's home.
ABRAMSON: Michael Smith had added insult to injury by placing harassing calls to his victims. So the cops installed what was known as a pen register at the phone company. The gadget recorded all the numbers Smith dialed and when he made them. It showed he was, indeed, behind those harassing calls.
KERR: And they used that information to get a search warrant, searched Smith's home, and then discovered that, in fact, he was the robber who was behind the harassment.
ABRAMSON: But police never got any sort of warrant to record those dialed numbers. So, Smith moved to have that evidence thrown out, saying it was a violation of his 4th Amendment right against unreasonable search and seizure. Law professor Orin Kerr says the high court ruled those numbers don't really belong to you.
KERR: The Supreme Court said that when you're dialing numbers, you're basically talking to the phone company, asking them to set up the call.
ABRAMSON: In other words, you've handed that dialing information over to a third party, to the phone company. So the police don't need a warrant, since they're not violating your privacy. And as the court likes to do, the ruling drew an analogy to an earlier, simpler time.
KERR: Before you could dial a phone, you'd pick up the phone and talk to Mabel, the telephone switchboard operator, and say, Mabel, you know, connect me to Pennsylvania 6-5000. And she would say OK.
ABRAMSON: And the police could get that information from Mabel without getting a search warrant for your home.
Thirty-four years after Smith, the government says much the same principle applies today, and allows it to collect much of the country's phone traffic. And that disturbs many people.
Law professor Jennifer Granick of Stanford University says it's a huge leap from the Smith case to the NSA order for all phone records.
JENNIFER GRANICK: Nothing in Smith versus Maryland authorizes mass surveillance, and the information that was collected in Smith versus Maryland is a much narrower category than the information that the government's currently getting.
ABRAMSON: Granick says Smith was talking about one guy suspected of a crime. But now the NSA is asking Mabel to report on nearly every call made in the U.S. And that's not all. Today, the quantity of metadata has exploded.
In 1979, the court could never have known that a ruling on phone records would expand to include Internet surfing records, credit card transactions, toll records, email traffic, tweets and Facebook postings.
Today, the government maintains that all that stuff is third party information. That includes what may be the most revealing information of all: cell phone tracking information. Your cell phone is constantly sending a signal, revealing where you are. Jennifer Granick says the availability of that location information gives a new and frightening significance to the Smith decision.
GRANICK: The records show things like you were at your house or you were at your office. These pieces of information are traditionally protected information under the 4th Amendment, and is not information that you voluntarily disclose to anybody.
ABRAMSON: But the courts have backed up the government here. Just last month, the Fifth Circuit said the government can get cell phone tracking information without a warrant. Once again, you should know that Mabel knows where you are when you carry a cell phone.
Civil libertarians have argued the courts should draw a line around what kind of metadata can be analyzed. But George Washington University law professor Orin Kerr says that's not the courts' role.
KERR: Hard for courts to craft that kind of line. Easy for Congress to just say, listen, when you get a court order for metadata, it can only be for a certain window of time, or a certain number of users.
ABRAMSON: There is some support in Congress for redrawing that line. That support could grow, because the amount of metadata is growing so quickly. So is the science of interpreting that data. A look at that in tomorrow's story. Larry Abramson, NPR News. Transcript provided by NPR, Copyright NPR.