Supreme Court Considers Whether to Grant Privacy to Cell Tower Location Records

Posted in: Constitutional Law

The U.S. Supreme Court recently granted review in Carpenter v. United States. This case raises important questions about the Fourth Amendment implications of the warrantless monitoring of a suspect’s location over a period of several months. The monitoring involved acquiring cell phone records that included information about roughly where a cell phone was located when a call was placed. In this column, I will critically examine several arguments for allowing such monitoring without a warrant or probable cause.

The Facts

In Carpenter, police suspected several men of committing a series of armed robberies. In addition to other incriminating evidence that they gathered against their suspects, police also successfully sought orders from magistrate judges directing the suspects’ wireless carriers to provide cell phone records. These records included, among other things, the approximate location of the suspects’ cell phones during an extended period of time spanning months (127 days for one of the suspects). The standard for acquiring the orders for these records was not “probable cause,” the term that appears in the Fourth Amendment, but “reasonable grounds to believe … the records are relevant and material to an ongoing criminal investigation.” The government subsequently used this evidence, over Fourth Amendment objections, to help show that petitioners were in the vicinity of various robberies when they took place. The evidence likely played a role in securing convictions related to those robberies.

Though the government had to meet a federal statutory standard, provided by the Stored Communications Act, to acquire the records in question, it notably did not have to show that it had probable cause to believe that the records would contain evidence that petitioners had committed crimes, the proper standard for acquiring a warrant when police intend to perform a Fourth Amendment “search.” The constitutional question presented by this case is therefore whether police are performing a “search” when they acquire cell phone records from wireless providers that contain information about a suspect’s cell phone location while being used during specified times, here spanning several months.

The Sixth Circuit Court of Appeals determined that what the government did, in ordering production of the cell phone records, did not constitute a Fourth Amendment “search,” and that the government therefore acted lawfully when it sought to acquire those records pursuant to a less demanding statutory standard than probable cause. The Supreme Court will be reviewing those arguments when it hears the case, so let us consider some of them here.

The Fourth Amendment Protects Only the Content of Communications

One of the appeals court’s rationales for ruling as it did involves the distinction between the content of private communications and the routing information connected with those communications. The court explained that when people engage in private communication, by telephone or by mail or email, the Fourth Amendment protects the words that they use in their communications with one another but does not protect the routing information for those communications. This means that the content of a letter or a telephone conversation or email—that is, the words written or spoken during the exchange—are protected by the Constitution. However, the information needed to connect the parties to each other is not protected, and this would include the mailing address (for letters), the email addresses (for emails), and the telephone numbers (for telephone calls). Most pertinently, the court cites Smith v. Maryland for the proposition that the government can, without first seeking a warrant or demonstrating probable cause, install a pen register on a phone line to reveal to the government all the numbers dialed from that line.

The court regards the content/routing distinction as relevant to this case, because the government did not in any way seek the contents of the cell phone conversations that petitioners had but instead sought records indicating where (geographically) the calls were coming from (or going to), a fact similar to what numbers are dialed from a particular phone line, as approved in Smith. The argument has a surface plausibility, but it has a problem. It assumes that petitioners are claiming privacy for cell phone locational records because such records reveal the route of private telephone conversations. That is, it assumes that the claimed privacy interest is in some important way tied to the fact that people were having private telephone conversations at the time that the data was created.

If petitioners’ claim were tied to the privacy of the telephone calls, then it would make sense to respond that routing information, as per Smith, is not protected by the Fourth Amendment; only the content of the conversations is protected. But petitioners are claiming a different sort of privacy interest, one that covers their own locations over a period of months, as revealed by data showing the locations of their cell phones at the times that calls were made. What is significant, then, is not anything particular to the privacy of telephone calls per se but is connected instead to the fact that a cell phone’s location exposes the location of the owner of that cell phone, given that people tend to keep their cell phones with them at all times. As the Supreme Court said in Riley v. California, “[n]ow it is the person who is not carrying a cell phone, with all that it contains, who is the exception.” As five justices found (in separate opinions) in United States v. Jones, an extensive record of where a person is located, even in public, can provide intimate information about that person that would not be available through casual observation. Monitoring a person’s location in public over time accordingly invades what a majority of the Court would most likely consider a reasonable expectation of privacy in a manner that would require a warrant based on probable cause.

Third Party Doctrine

A second basis that the court provides for refusing to recognize a Fourth Amendment interest in this case is known as the third party doctrine. This doctrine provides that if the government requires a third party to surrender information that a suspect has voluntarily conveyed to that third party, then no Fourth Amendment search has occurred. This means that the government may obtain an individual’s bank records from the bank she uses without triggering application of the Fourth Amendment, as per United States v. Miller. This is because the individual voluntarily shared the financial information with the bank and thereby forfeited any privacy interest in that information (at least as against the government), and the government could therefore order the conveyance of that information without violating the privacy of the individual.

Only if the bank itself had a personal privacy interest in the information could it assert a Fourth Amendment right, and the bank lacks any such interest, so no one has a Fourth Amendment right that would require the government to get a warrant based on probable cause before ordering production of the bank records.

In our case, too, the government sought records from a third party—the wireless providers at issue—rather than directly from petitioners. Petitioners necessarily shared their locational information with their wireless providers each time they made or took a call, thereby forfeiting a privacy interest in that information. The wireless providers, in turn, almost certainly lack any privacy right in the records associated with their customers’ calls. Therefore, it follows that the government could seek the locational information it sought via an order without probable cause and a warrant, without implicating the Fourth Amendment right against unreasonable searches.

This argument is harder to defeat than the first because it does not rest on a misinterpretation of petitioners’ claimed privacy right. It instead rests on Supreme Court doctrine. The doctrine, as I suggest at length in What Is A Search? Two Conceptual Flaws in Fourth Amendment Doctrine and Some Hints of a Remedy, is quite problematic because sharing information with one third party—especially a third party that will be keeping that information private from others—should not reasonably be read as a forfeiture of privacy.

The third party doctrine treats two acts as equivalent when they are not at all equivalent. The first act is a decision to knowingly expose one’s private thoughts or actions to the public, for example, by yelling out personal information while sitting in a crowded subway car. If a police officer hears what the person yells, she need not cover her ears until she has acquired a warrant or probable cause, because the person who yells does legitimately knowingly expose his private thoughts to the public (including the police).

The second act (which the third party doctrine equates with the first) is the voluntary sharing of information with one third party. By that act of exposing oneself to one third party, the Supreme Court has said, one forfeits one’s privacy against the world such that police may order that information from the third party without having to satisfy any of the demands of the Fourth Amendment. However, the reality is that sharing information with one third party does not, on any meaningful reading, represent a decision to share the information with the world, in the way that yelling private thoughts on a subway train does. In addition, in a modern society, it is virtually impossible to carry on one’s daily activities without disclosing personal information to some third party, whether it be an internet service provider, a bank, or the people who collect one’s garbage each week.

In her opinion in Jones, Justice Sotomayor questioned the third party doctrine in similar terms. She said:

[I]t may be necessary to reconsider the premise that an individual has no reasonable expectation of privacy in information voluntarily disclosed to third parties. This approach is ill suited to the digital age, in which people reveal a great deal of information about themselves to third parties in the course of carrying out mundane tasks … I would not assume that all information voluntarily disclosed to some member of the public for a limited purpose is, for that reason alone, disentitled to Fourth Amendment protection.

Justice Sotomayor may have four other votes for rejecting the third party doctrine, a doctrine that ought, from a logical and normative perspective, to be rejected.

Cell Tower Locational Data Not That Precise

The court of appeals distinguishes Carpenter from Jones in two key ways. In Jones, a majority of the Court held that attaching a GPS to a suspect’s car and thereby tracking the suspect’s movements in the car constitutes a search subject to the Fourth Amendment’s warrant requirement.

First, the appeals court noted that police in Jones trespassed on a private individual’s vehicle by attaching a GPS to it, whereas the government in Carpenter simply solicited phone records of locational data that were voluntarily surrendered to the wireless providers by the suspects when they used their cell phones. I already discussed the weakness and potential legal vulnerability of the third party doctrine above. We might add to this the fact that the Jones majority’s view—that what makes long-term locational monitoring through a GPS intrusive is the trespass involved in attaching a small GPS device to a suspect’s car—is wholly unconvincing. The four-justice concurring opinion’s view—that what is objectionable about attaching a GPS device is the long term monitoring itself, regardless of how the police were able to accomplish that monitoring—is far more compelling (and seemed to have persuaded Justice Sotomayor, despite her having joined the majority opinion).

The second distinction from Jones that the appeals court draws has to do with the precision of a GPS monitoring device as compared to the imprecision of locational monitoring enabled by cell phone tower data. According to the court of appeals, “this is not a GPS-tracking case. GPS devices are accurate within about 50 feet,” whereas “the cell-site data … could do no better than locate the defendants’ cell phones within a 120- (or sometimes 60-) degree radial wedge extending between one-half mile and two miles in length.” Summing up the distinction between the two monitoring approaches, the court says that cell site data are “as much as 12,500 times less accurate than the GPS data in Jones.”

Does this matter? Justice Sotomayor emphasized in her concurring opinion in Jones her worry that GPS data about an individual over time could tell a story of trips to “the strip club, the criminal defense attorney, the by-the-hour motel, the union meeting, the mosque, the synagogue or church, the gay bar and on and on….” With a far less precise monitoring tool, such as the cell site data, such a story might not emerge. A locational identification could be consistent with the target going into any of a large number of buildings, thus leaving the observer unaware of the intimate story of the person’s life.

I find this argument potentially convincing, although I worry that over time, cell site locational data may become more accurate. I also believe, with the appeals court concurring opinion, that “the sheer quantity of sensitive information procured without a warrant in this case raises Fourth Amendment concerns of the type the Supreme Court … acknowledged in United States v. Jones.” In other words, monitoring even imprecisely over a period of many months may help the observer zero in on exactly what the target was doing and where he was going at any given time.

I would analogize the imprecision point to the argument that the Supreme Court rejected in Kyllo v. United States. Kyllo concerned the use of a heat detection device to discern the heating patterns emerging from a targeted home and whether that conduct implicated the Fourth Amendment. One argument that ultimately did not carry the day was that such heating patterns do not really tell us very much at all about what is going on in the house—they are not precise in the way that an X-ray camera directed at the house would be. Notwithstanding this imprecision, however, the Court treated use of the thermal detection device on the home as a Fourth Amendment search requiring a warrant.

In Carpenter, of course, the home—the most important site of privacy, under the Court’s doctrine—is not involved. Instead we have a person’s movements in public, which are in general not considered private for Fourth Amendment purposes, as per United States v. Knotts. But the point I would make is that in both the cell site case and the GPS case, potentially private information becomes available to the government in virtue of long-term monitoring of a person’s location in public. To the extent that the Supreme Court apparently has five votes for recognizing that GPS use implicates Fourth Amendment concerns, despite its monitoring a person’s location in public, the Court might similarly find—as it did in Kyllo—that even a less precise version of the GPS implicates those concerns as well, especially when extensive monitoring may make up for the imprecision in each data point.


It is hard to know what the Supreme Court will do with this case. One might predict a positive outcome for the petitioners because they lost below and the Court took the case. Yet the case is an important one that asks, among other things, whether the presence or absence of the trespass involved in police attaching a GPS device to a vehicle truly disposes of the Fourth Amendment issue there. The Court may wish to answer that question and may have taken the case for that reason, even if it agreed with how the lower court answered it.

In a way, this is an imperfect case. It might have been better if the Court had taken a case in which a private person, a friend of the suspect, without police bidding, attached a GPS to the suspect’s vehicle and then handed over the GPS data to the police, after being ordered to do so. Then the Court could revisit its reasoning in Jones along with the third party doctrine’s viability without also having to contend with the reduced precision involved in cell site monitoring versus GPS monitoring.

Yet such a case would be anomalous. Cell site data collection by wireless providers, by contrast, is ubiquitous, and we therefore want to know whether police can demand such data routinely without having to acquire a warrant or probable cause. We have an interest in getting answers to questions that come up all the time, even if they are not the purest and cleanest questions.

The imprecision point is, I think, the strongest point for the government. I would, however, still find that the cell site data demand is a search, rejecting the third party doctrine once and for all and noting as well that collecting even imprecise data over time can add up to a precise picture of what is going on. I am pleased that the Court has decided to take on this issue for resolution, as it is significant and may affect the privacy of just about everyone, because almost everyone has a cell phone and thereby exposes (approximately) where she is at close intervals every single day. Whenever we use our cell phones, it would be useful to know whether we are thereby exposing our location to the police (and not just to our wireless providers).

  • Joe Paulson

    The Knotts ruling left open the possibility that a 24/7 monitoring situation would be a matter of concern. Five justices in U.S. v. Jones supported general expectation of privacy v. Scalia’s property approach being the test. A case like this might bring us back to that question without the clear property right found there.

    Also, guess if the government felt the location data was useful, there is some concern for it being a violation of privacy. Even if it wasn’t pinpoint. After all, the government felt it useful to know and the same would be the case in other cases. There are certain locations, especially if you are there repeatedly, many rather not even be found near. Anyway, as you say, the third party doctrine is bogus.

  • TZ

    It seems that in future cases police could be using cell phone GPS data from third parties such as Map, photo and search apps. This data is very precise and not just available from cell phone providers. The third party doctrine would work to make the 4th amendment requirement for probable cause almost null and void.