In the course of executing its various functions, a cell phone continually searches for the best signal and typically connects to the nearest site of radio antennas on towers or other locations, called cell sites. With every connection, a time-stamped record is created. The record generated is called “cell-site location information” or CSLI. This information is used and stored by wireless carriers for business purposes. Location precision deriving from CSLI information depends on the size of the geographic area covered by the cell site.  As the number of cell sites has increased to handle increasing data demands, coverage areas have shrunk. Consequently, cell phones today give rise to large amounts of increasingly precise CSLI. The United States Supreme Court discussed issues arising from these developments on June 22, 2018, in the case of Carpenter v. United States 2018 U.S. LEXIS 3844 (U.S. June 22, 2018).  In a 5-4 decision, the Supreme Court held that the Government’s acquisition of a plaintiff’s cell phone cell-site location information from his wireless carriers constituted a Fourth Amendment search that required a warrant supported by probable cause.


In 2011, police arrested several men suspected in a series of robberies in Detroit. One of the suspects identified over a dozen accomplices involved in nine robberies in Ohio and Michigan over a four-month period. In addition, the suspect provided cell phone and other information that eventually led prosecutors to identify plaintiff Timothy Carpenter as a suspect. Prosecutors obtained court orders under the Stored Communications Act[1](“SCA”) to access Carpenter’s cell phone records.  The SCA enables the Government to compel the disclosure of certain telecommunications records when it “offers specific and articulable facts showing that there are reasonable grounds to believe” that the records sought “are relevant and material to an ongoing criminal investigation.”  18 U.S.C. section 2703(d).  Wireless carriers produced Carpenter’s CSLI information over a four-month period, which included 12,898 location points specifying Carpenter’s movements for an average of 101 data points per day.

Carpenter was charged with several counts of robbery and firearms violations. Before trial, Carpenter moved to suppress the CSLI data.  He argued that the Government seized CSLI records without securing a warrant supported by probable cause, thereby violating his Fourth Amendment rights.  The District Court denied the motion.  Prosecutors used the records at trial to show that Carpenter’s phone was near some of the robbery locations when those robberies occurred. Carpenter ultimately was convicted.

The Sixth Circuit Court of Appeals affirmed the conviction, holding that Carpenter lacked a reasonable expectation of privacy in the location information collected by the FBI because he had voluntarily shared that information with his wireless carriers. The Court of Appeals determined that Carpenter effectively volunteered this information in that he chose to use a cell phone and had accepted that cell phones operate by providing cell-site data to the carriers’ sites. Carpenter sought review from the Supreme Court.

The Supreme Court granted certiorari to determine “whether the Government conducts a search under the Fourth Amendment when it accesses historical cell phone records that provide a comprehensive chronicle of the user’s past movements.”


The Court began by noting that the Fourth Amendment’s protections against unreasonable searches and seizures by police and other Government officials were historically connected to common-law trespass – officials were generally proscribed from physically intruding on an individual’s constitutionally protected property in search of evidence of criminal activity. In Katz v. United States,[2] the Supreme Court extended Fourth Amendment protections beyond property interests to protect certain expectations of privacy. Katz established that when a person “seeks to preserve something as private,” and his expectation of privacy is “one that society is prepared to recognize as reasonable,” official intrusion into that area generally qualifies as a search and requires a warrant supported by probable cause.[3]

The Court observed that the process of determining which expectations of privacy were entitled to protection was influenced by what the Constitution’s creators would have considered an unreasonable search and seizure at the time of the Fourth Amendment’s adoption. The Court explained that key considerations in this determinative process were guarding “the privacies of life” against “arbitrary power,”[4] and putting “obstacles in the way of a too permeating police surveillance.”[5] Such considerations continue, the Court explained, as innovations in surveillance tools progress.[6]  In Riley v. California,[7] the Court noted the “immense storage capacity” of cell phones in holding that police officers must generally obtain a warrant before searching the contents of a phone.

The Court explained that the issue of personal location information maintained by a third party had not yet been specifically addressed by precedent, yet two lines of cases informed the privacy interests at stake. The first set involved a person’s privacy expectation in his physical location and movements.  In United States v. Jones,[8] five Justices said that conducting GPS tracking of a cell phone would raise privacy concerns. They noted that “every movement” a person made would be tracked, and that such monitoring used over a longer period than the 28 days in Jones during criminal investigations would generally “impinge[] on expectations of privacy” even if those movements were disclosed to the public at large.

The Supreme Court next discussed the second line of cases which involved a person’s expectation of privacy in information voluntarily turned over to third parties. The Court explained that Government officials are generally free to obtain such information from recipient third parties without triggering Fourth Amendment protections. This is known as the “third-party doctrine.”  In United States v. Miller,[9] bank deposit slips, canceled checks, and monthly statements that the Government sought in a tax evasion investigation were considered by the Court to be “business records.”  These were not confidential communications but of use in the “ordinary course of [banking] business,” and thus could not have been expected by the defendant to be kept private. The defendant also could not claim ownership or possession of these documents since they were “business records.” And in Smith v. Maryland,[10] the Supreme Court held that there was no expectation of privacy in records of dialed telephone numbers conveyed to the phone company; using a phone to place a call meant the caller assumed the risk that those numbers would be revealed to the police.

The Court here observed that CSLI tracking was very similar to GPS tracking in that information thus collected was comprehensive, detailed, and effortlessly compiled. On the other hand, “the fact that the individual continuously reveals his location to his wireless carrier implicates the third-party principle of Smith and Miller.”

The Court rejected the Government’s contention that CSLI records were “business records,” noting 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.” The Court noted that cell phones were ubiquitous, are typically kept on or very near to a person’s body or clothing, often taken everywhere they go, and provide large amounts of information. An individual’s privacy expectations with such information, imbued with the privacies of life, would be of a completely different level than the privacy expectations with the documents in Miller or the phone numbers in Smith.  The Court also determined that such information was not truly volunteered with third party carriers because cell phone use was such an indispensable part of modern life and “log CSLI without any affirmative act by the user.” Should the third-party doctrine apply, the Government would have “near perfect surveillance” of a person and allow it to go back in time to retrace their whereabouts.  Further, with advances in location precision ever-increasing, the Court noted that it had held previously that it “must take account of more sophisticated systems that are already in use or in development.”[11]

The Supreme Court declined to extend Miller and Smith to CSLI collection, and concluded that that because of the unique nature of cell phone location information, the third-party doctrine did not apply.  The Court determined that the Government’s acquisition of Carpenter’s CSLI was a Fourth Amendment search. The Court correspondingly held that the Government must generally obtain a warrant supported by probable cause before acquiring CSLI records.

This Court explained that its decision was narrow. The Court said it did not disturb the application of Smith and Miller or call into question conventional surveillance techniques and tools, such as security cameras.  Obtaining such information in real-time was not addressed, according to the Court.  Nor did its opinion address other business records that might incidentally reveal location information, nor impact other collection techniques involving foreign affairs or national security.

Here, because the Government did not obtain a search warrant supported by probable cause for the historical CSLI, the Court found that Carpenter’s reasonable expectation of privacy in the sum of his physical movements was violated when the Government acquired his CSLI data from the carriers. Accordingly, the Supreme Court reversed the Sixth Circuit’s judgment, and remanded.


Each of the four opposing Justices offered dissents. Justice Kennedy, joined by Justices Alito and Thomas, said the majority came up with an unworkable line and improperly removed CSLI from other types of information; property rights as the basis for reasonable expectations of privacy was the correct anchor in such cases and the third-party doctrine should apply here. Justice Alito, joined by Justice Thomas, said that the SCA should have sufficed to obtain CSLI records, not the Fourth Amendment. Not doing so created a “crazy quilt” of the Fourth Amendment.  Justice Thomas wrote that the reasonable expectation of privacy concept should be reconsidered entirely. Justice Gorsuch, writing alone, wanted to eliminate both the third-party doctrine and the reasonable expectation of privacy as standards in favor of a concentration on whether an individual maintains a property interest, focusing on the determination of ownership of that property, as challenging as that determination might be.


With Carpenter, the Supreme Court has established that law enforcement officers will typically need a warrant supported by probable cause to obtain historical CSLI records. Before this decision, the lower threshold was the one in SCA’s Section 2703(d), which requires showing “reasonable grounds” to show that the sought-after records are “relevant and material to an ongoing investigation.”  While a warrant is not required in all such cases, for example, where exigent circumstances or other exceptions to the warrant requirement apply, agencies will find it more challenging to obtain such information in the course of investigations. It should also be emphasized, however, that the Court explicitly noted the narrow nature of its decision.  The Court stated, “We do not express a view on matters not before us: real-time CSLI or ‘tower dumps’ (a download of information on all the devices that connected to a particular cell site during a particular interval).”  Decisions concerning whether a law enforcement officer must obtain a warrant to access these types of data remain unanswered at this time.

As always, if you wish to discuss this matter in greater detail, please feel free to contact me at (714) 446–1400 or via email at jrt@jones-mayer.com.

Information on www.jones-mayer.com is for general use and is not legal advice. The mailing of this Client Alert Memorandum is not intended to create, and receipt of it does not constitute, an attorney-client-relationship.

[1] 18 U.S.C. 2701, et seq.

[2] 389 U. S. 347 (1967).

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

[4] Boyd v. United States, 116 U. S. 616 (1886).

[5] United States v. Di Re, 332 U. S. 581 (1948).

[6] Kyllo v. United States, 533 U. S. 27 (2001).

[7] 134 S. Ct 2473 (2014).

[8] 565 U.S. 400 (2012).

[9]  425 U. S. 435 (1976).

[10]  442 U. S. 735 (1979).

[11] Kyllo, 533 U. S., at 36.