Carpenter v. U.S.: Obtaining Extensive Cell Site Location Data is a Search

by Jack E. Call, Professor of Criminal Justice, Radford University, E-mail:

               On June 22, 2018, as the 2017-18 term wound down, the Supreme Court released its long-awaited decision in Carpenter v. U.S.[1]  The Court held, 5-4, that when the police obtain cell site location information (CSLI) about a person’s cell phone usage, that action constitutes a search under the Fourth Amendment.  The Court held further that the Fourth Amendment requires that the police utilize a warrant to obtain this information from a cellular service provider.

Background of the Case

               The Detroit police were investigating a string of robberies of Radio Shack and T-Mobile stores in the city.  After arresting a suspect, that suspect implicated Timothy Carpenter in the robberies.  In accordance with the provisions of the Stored Communications Act, the police obtained a court order that instructed Carpenter’s cell phone providers to turn over to them 159 days of cell site location information.  This information gave the police the locations of the cell towers with which Carpenter’s phones were communicating on the days of the robberies.  The CSLI data for Carpenter placed him in the vicinity of four of the robberies at the times of their commission.  Carpenter argued that this evidence was inadmissible because the police were conducting a search when they obtained this information.  He argued further that the search was improperly conducted because the police needed a search warrant to obtain the CSLI information, rather than the court order authorized by the Stored Communications Act.[2]

               When a cell phone is turned on, it is constantly seeking communication with the closest cell tower.  This communication takes place even when the cell phone user is not using the phone to text, make a call, access the internet, or utilize email.  The cell tower keeps a record of all successful communications of a phone with that tower, and cellular service providers keep those records for five years. In more sparsely populated areas, a cell phone connection to a particular cell tower may only place the phone within a 2-mile radius of the tower.  However, in more densely populated areas, where there are more cell towers, CSLI may locate a particular cell phone within an area as small as a dozen city blocks.

The Court’s Decision

               Chief Justice Roberts wrote the opinion for the five Justices in the majority.  He began by suggesting that two lines of cases are at work in this case.  The first line of cases deals with the extent of privacy that an individual possesses in his physical location and movements.  The Court has recognized that a “person traveling in an automobile on public thoroughfares has no reasonable expectation of privacy in his movements from one place to another.”[3]

However, five Justices have also recognized recently that the situation will be viewed differently when the police follow a person’s movements over an extended period of time.  In U.S. v. Jones,[4] those five Justices took the position that using a GPS device to monitor the movements of a defendant’s car for 28 days infringed upon the defendant’s reasonable expectation of privacy and was therefore a search.[5]

        The second line of cases involves the so-called third party doctrine.  The Supreme Court has held that it is not a search under the Fourth Amendment when the police obtain a record of deposits made into a bank account in U.S. v. Miller[6] or a list of the phone numbers called from a particular phone over a period of time in Smith v. Maryland.[7]  The basis for these holdings is that when a person shares information with a third party, the person has forfeited their privacy interest in the information and has assumed the risk that the third party will share the information with others.

The government argued, of course, that the third party doctrine dictated the appropriate outcome in this case.  When Carpenter turned on his phone, they argued, he shared the general location of his phone with his cell phone provider and assumed the risk that the provider would share that information with others.

Chief Justice Roberts recognized the apparent relevance of the third party doctrine.  However, he also indicated that “it is not clear whether [the logic behind the third party doctrine] extends to the qualitatively different category of cell-site records.”  The difference is the scope and pervasiveness of CSLI.  The Chief Justice pointed out that “[t]here is a world of difference between the limited types of personal information addressed in Smith and Miller and the exhaustive chronicle of location information casually collected by wireless carriers today,” information that is retained by cell phone providers for years.

The Court also addressed the issue of the voluntariness of sharing CSLI with the cell phone provider.  One of the rationales behind the third party doctrine is that one assumes the risk that financial information and phone numbers called will be shared with others by banks and phone companies because one voluntarily shares this information with those institutions.  Roberts noted that the use of cell phones is such “a pervasive and insistent part of daily life” that cell phone users cannot be said in any “meaningful sense” to have voluntarily assumed the risk that cell phone providers would share CSLI with others.  Given the heightened sensitivity of CSLI, it should normally be obtained only with a warrant.

               As is typical with groundbreaking decisions like Carpenter, the opinion raises more questions than it answers.  For example, Roberts was careful to point out that the Court’s decision expresses no opinion as to whether the government needs a warrant to obtain “real-time CSLI ….. information or [a list of] all the devices that connected to a particular cell site during a particular interval…”  Roberts also suggested that exigent circumstance, such as “bomb threats, active shootings, and child abductions,” might well justify dispensing with a warrant requirement.

The Dissenters

               All four of the dissenting Justices – Kennedy, Alito, Thomas, and Gorsuch – wrote dissenting opinions (although some of them joined the opinions of the other dissenters as well).  Notably, Thomas and Gorsuch would abandon the reasonable expectation of privacy definition of a search established in Katz v. U.S.[8]   

For years, the Court held that the definition of a search under the Fourth Amendment was whether the police had physically intruded into a constitutionally-protected area, a definition that is often referred to as a trespass approach.  Katz involved the attachment of an eavesdropping device to the outside of a glass telephone booth.  Since the eavesdropping device did not physically intrude into the phone booth, its use would not have been considered a search under the trespass approach.  However, a majority of the Justices recognized in Katz that advances in technology had made it possible to intrude substantially into the privacy of individuals without a physical trespass.  In the final analysis, the Court said in Katz, the Fourth Amendment was designed to “protect people, not places.”  Therefore, the police conduct a search whenever they do something that intrudes upon a reasonable expectation of privacy, whether or not a physical trespass takes place.

               It seems fair to say that most students of the Fourth Amendment understood Katz as replacing the trespass approach with the reasonable expectation of privacy approach.  Then, in the Jones case, many (if not most) Fourth Amendment observers were surprised when the Court held that the police conducted a search when they attached the GPS device to Jones’ automobile.[9]  As mentioned earlier, a majority of the Justices based this conclusion on the physical intrusion into the car that occurred when the GPS device was attached to it.  These Justices made it clear that the reasonable expectation of privacy approach as to what constitutes a search was an alternative definition of search, rather than a replacement of the trespass approach.

               In their Carpenter dissents, Thomas and Gorsuch both expressed dissatisfaction with the reasonable expectation of privacy approach and would overturn Katz.  If a majority of the Court adopted this position, it would call into question many cases in which the Court has used the reasonable expectation of privacy approach to determine whether police action constituted a search.

               Justice Kennedy’s dissenting opinion was joined by Justices Alito and Thomas.  His opinion is based largely on a defense of the third party doctrine.  “Customers like [Carpenter] do not own, possess, control, or use [their cell phone] records, and for that reason have no reasonable expectation that they cannot be disclosed pursuant to lawful compulsory process.”  While Kennedy did not specifically suggest that the reasonable expectation of privacy approach to what constitutes a search should be abandoned, he did indicate that “[t]his case should be resolved by interpreting accepted property principles as the baseline for reasonable expectations of privacy.”  The reference to “accepted property principles” suggests that he (and presumably Justice Alito) might be persuaded to abandon the reasonable expectation of privacy approach in favor of the trespass approach.  If so, that would provide four votes for abolition of the reasonable expectation of privacy approach.[10]

Carpenter’s Impact on the Future

               Carpenter represents the second recent opinion from the Court that expresses concern about the impact of new technologies on individual privacy.  In Riley v. California,[11] the Court held that the police, under normal circumstances, need a warrant to search the contents of a cell phone found on a person who has just been arrested.  Of course, the police may search a person arrested and the area within his immediate control without a warrant for a weapon or evidence of a crime without any reason to think the search will turn up a weapon or evidence.[12]  While a proper search incident to arrest would almost certainly permit opening a briefcase carried by the person arrested or opening an appointment book found on the arrestee, the Court (in an opinion written by Chief Justice Roberts) recognized in Riley that the amount of highly personal information contained on the typical cell phone vastly exceeds the amount of such information contained in a briefcase or an appointment book.  Therefore, the Court required that the police obtain a warrant before browsing through the contents of a cell phone.[13]

               Obviously, Carpenter and Riley share a concern about the impact of new technologies on individual privacy.  The two cases also demonstrate a concern that Fourth Amendment rules from earlier Supreme Court decisions, when the ramifications of newly emerging technology were not anticipated, may not be applied to situations involving new technology in a literal way.  For example, a literal application of the search-incident-to-arrest rules established by Chimel and Robinson would have permitted a search of Riley’s cell phone without a warrant.  Those rules permit a warrantless search of the person arrested and items found on the person.  The cell phone was an item found on Riley’s person.

               Carpenter and Riley represent a clear departure from the literal application of the search-incident-to-arrest rule and the third party doctrine.  Whenever the Court deviates from what appears to be a logical extension of existing rules, the result is usually some confusion stemming from a lack of clarity.  This is an inherent difficulty in our judicial process.  The Supreme Court creates rules incrementally, one case at a time.  Filling in the gaps not only takes time, but the process never really ends.  Most Supreme Court cases answer one question, but the answer frequently raises new questions.  The Court undoubtedly recognizes that their decisions in Carpenter and Riley have created a good deal of uncertainty for law enforcement officers.  It can be expected (or at least hoped) that this recognition by the Court will result in its acceptance of other cases in the near future that will permit the Court to reduce some of this uncertainty.



[1] Carpenter v. United States, 585 U.S. _____ (2018).

[2] The court order permitted under the Stored Communications Act only required that the government make a showing that the evidence obtained by the order is relevant and material to a criminal investigation.  This is a much easier standard to satisfy than the showing of probable cause to think a search will reveal evidence of a crime that is required for a search warrant.

[3] United States v. Knotts, 460 U.S. 276 (1983), p. 281-82.

[4] United States v. Jones, 565 U.S. 400 (2012).

[5] The Jones case can be viewed as having two holdings (see Call, “Supreme Court Rules on Use of GPS Devices as Searches,” Virginia Police Legal Bulletin, Vol. 7, No. 1, August 2012).  The issue in the case was whether the police conducted a search when they installed a GPS tracking device on the outside of Jones’ car and used the device to track the car’s movements for 28 days.  Justice Scalia wrote an opinion for the Court, holding that installation of the device on the car was a search because it constituted a physical intrusion into a constitutionally-protected area.  Justice Sotomayor provided the fifth vote for this position in a concurring opinion.  In a concurring opinion written by Justice Alito, the other four Justices found that use of the GPS device was a search because using that device to monitor the car’s movements for such a long period of time intruded upon a reasonable expectation of privacy.  Justice Sotomayor also agreed with Justice Alito’s approach in her concurring opinion (although there are suggestions in her opinion that she might have been willing to go even further than these four Justices).  Not everyone agrees that the Alito approach should be considered a binding holding in Jones.  Chief Justice Roberts avoids this issue in Carpenter by simply stating that five Justices viewed the extended monitoring of Jones’ movements as a search.  Interestingly, Chief Justice Roberts was not one of the five Justices who took this approach in Jones.

[6] United States v. Miller, 425 U.S. 435 (1976).

[7] Smith v. Maryland, 442 U.S. 735 (1979).

[8] 389 U.S. 347 (1967).

[9] Supra, note 4.

[10] Of course, since Justice Kennedy has now retired from the Court, his potential willingness to abandon the Katz approach has become largely irrelevant.  However, it would not be surprising if his replacement (most likely Judge Brett Kavanaugh) shares the same dissatisfaction with the reasonable expectation of privacy approach expressed by Justices Thomas and Gorsuch.

[11] 573 U.S. _____ (2014).

[12] Chimel v. California, 395 U.S. 752; United States v. Robinson, 414 U.S. 218 (1973).

[13] See Call, “The Supreme Court Rules on Searches of Cell Phones Incident to Arrest,” Virginia Criminal Justice Bulletin, Vol. 10, No. 1 (January 2015) for a more in-depth discussion of Riley.