On June 22, 2018, the Supreme Court held, in Carpenter v. United States, that a warrant is required before a wireless telephone service provider may be compelled by a governmental entity to turn over its customer’s “historical” Cell Site Location Information (CSLI). 
In 2011, the police arrested four men for a series of armed robberies in Detroit, Michigan. One of them confessed that he had participated in the robbery of nine stores in Michigan and Ohio. He provided cell phone numbers for some of the other participants, including Timothy Carpenter. Under the Stored Communications Act (SCA), the government obtained orders directing the wireless service providers to turn over records for those cell phone numbers. The records included cell site location information for the target telephones at call origination and at call termination for incoming and outgoing calls. The government intended to use the CSLI to prove that Carpenter was in the vicinity of each of the robberies at the time it was committed. MetroPCS produced records for defendant Carpenter covering a period of 127 days, and Sprint produced records for two days, for “roaming” charges that were incurred while Carpenter was driving in Ohio.
Defense counsel moved to suppress, citing U S. v. Jones, and arguing that before the government may collect such data, the Fourth Amendment requires that it obtain a search warrant, pursuant to a showing of probable cause. In Jones, the Supreme Court had held that the 4th Amendment was violated when the police recorded the defendant’s movements for twenty-eight days with a GPS tracking device that they had secretly attached to his car. The District Court in Carpenter rejected defense counsel’s argument, and denied suppression. It held that the government’s collection of cell-site records, created and maintained by defendant’s wireless carrier, was not a “search” within the meaning of the Fourth Amendment. The “historical” CSLI was admitted into evidence at Carpenter’s trial, and he was convicted of several robberies and related charges.
The Sixth Circuit Court of Appeals agreed that the collection of CSLI was not a “search,” and it affirmed. However, the Supreme Court reversed, holding that the government’s acquisition of Carpenter’s cell-site records was a Fourth Amendment “search,” and that the collection of cell-site data did require a warrant.  Citing Katz v. United States, it explained that the Fourth Amendment protects not only property interests but certain expectations of privacy as well.  In Katz, the Court had held that it was a violation of the 4th Amendment to attach an electronic listening and recording device to the outside of a public telephone booth without a warrant.  The reasoning was that when an individual “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 sphere generally qualifies as a search and requires a warrant supported by probable cause. 
The Supreme Court explained that the digital data at issue in Carpenter – personal location information maintained by a third party – does not fit neatly under existing precedents but lies at the intersection of two lines of cases. One line holds that a person has a reasonable expectation of privacy in his physical location and movements, i.e., Jones  (GPS tracking device on car); and the other holds that there is no reasonable expectation of privacy in information voluntarily turned over to third parties, e.g., Smith v. Maryland  (records of dialed telephone numbers held by telephone company) and United States v. Miller (financial records held by bank).
The Court considered the fact that tracking a person’s past movements through CSLI is similar to the GPS monitoring in Jones, in that it is “detailed, encyclopedic, and effortlessly compiled,” but it also implicates the third-party principle of Smith and Miller in that the individual is continuously revealing his location to the wireless carrier. Ultimately, the Court decided not to extend Smith and Miller to cover cell-site records, because of their unique, revealing nature. 
A majority of the Court had previously recognized in Jones that individuals have a reasonable expectation of privacy in the whole of their physical movements, because they can reveal many private details of an individual ‘s life, not unlike the contents of the smart phone in Riley v. California. In fact, historical cell-site records present even greater privacy concerns than the GPS monitoring in Jones, because they give the Government near perfect surveillance, and allow it to travel back in time to retrace a person’s whereabouts . The only limit on how far back the government could search is the retention policies of wireless carriers, which for most of them is presently five-years. 
The Court acknowledged the Government’s contention that CSLI data is less precise than GPS information, but observed that the prosecutor thought the data accurate enough to highlight it during closing arguments in Carpenter’s trial. Moreover, the accuracy of CSLI is rapidly approaching GPS-level precision, and whatever rule the Court adopts “must take account of more sophisticated systems that are already in use or in development” (citing Kyllo ).  In Kyllo, it was held that use of a thermal imager to detect persons inside a residence was a “search” that required a warrant.
The Government had contended that the third-party doctrine governed the case because cell-site records are “business records,” created and maintained by wireless carriers, not unlike the records in Smith and Miller. But the Court pointed out that Smith and Miller had also considered “the nature of the particular documents sought” and limitations on any “legitimate ‘expectation of privacy’ concerning their contents.” (Miller  ). In the Court’s view, there was “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.” 
It further stated that the second rationale for the third-party doctrine – voluntary exposure – also does not apply, because cell phone location information is not truly “shared” as the term is normally understood. Cell phones and the services they provide are “such a pervasive and insistent part of daily life” (Riley) that carrying one is “indispensable to participation in modem society.” Moreover, a cell phone automatically logs a cell-site record, without the user having done anything beyond turning it on. “Apart from disconnecting the phone from the network, there is no way to avoid leaving behind a trail of location data.”
The Court concluded that the government’s acquisition of the cell-site records was a “search” within the meaning of the Fourth Amendment, and that the Government was obligated to obtain a warrant supported by probable cause. “[R]easonable grounds” for believing that records are “relevant and material to an ongoing investigation” (18 U.S.C. §2703[d]), “falls well short of the probable cause required for a warrant.” Thus, an order obtained under §2703[d] of the SCA is not a permissible mechanism for accessing historical cell-site records.
Inexplicably, the Supreme Court never mentions in Carpenter that there is another section of the SCA which expressly provides for the collection of communications records through the use of a warrant. (§2703[c][l ][A]). The warrant provision was noted in the concurring opinion in the Circuit Court, which stated that the issue is “not whether the cell-site location information (CSLI) for Carpenter *** could have been obtained under the Stored Communications Act (SCA),” but “whether it should have been sought through provisions of the SCA directing the government to obtain a warrant with a probable cause showing, 18 U.S.C. § 2703(c)(l)(A), or a court order based on the specified ‘reasonable grounds[,]’ id. §§ 2703(c)(l)(B), (d).” 
The Supreme Court characterized its holding in Carpenter as “a narrow one,” stating that it does not disturb the application of Smith and Miller, or call into question conventional surveillance techniques and tools, such as security cameras. It does not address other business records that might incidentally reveal location information; and it does not consider other collection techniques involving foreign affairs or national security. The opinion also does not address “real-time” cell-site information.
The opinion leaves open the question of whether a warrant will be required for “short term” CSLI. As noted above, two days of CSLI were provided by SPRINT, out of the seven days which were requested. The Sixth Circuit had previously held, in Skinner, that it was not unreasonable for authorities to track the defendant’s cell phone for three days, using its GPS technology, pursuant to a court order which authorized the telephone company to provide such data. It distinguished such “short term” monitoring from the “long term” GPS monitoring in Jones. In Carpenter, the Supreme Court stated that it was “sufficient for our purposes today tohold that accessing seven days of CSLI constitutes a Fourth Amendment search.”  (emphasis supplied). It rejected the suggestion in Justice Kennedy’s dissenting opinion, that it was deciding the “limited period for which the government may obtain an individual’s CSLI free from Fourth scrutiny,”
Although the Court states that the Government will generally need a warrant to access CSLI, it acknowledges that case-specific exceptions, such as exigent circumstances, may support a warrantless search. Another recognized exception to the warrant requirement is that the government acted in “good faith” in reliance upon a statute, which may apply even if the statute is subsequently declared unconstitutional. In the Sixth Circuit, the concurring opinion stated that the authorities had acted in the “good faith” in implementing the Stored Communications Act; and therefore, suppression had been properly denied, even though there had been a Fourth Amendment violation. If the prosecution asserted the “good faith” exception in the lower Court, suppression could be denied on that alternative ground on remand.
1. Carpenter v. United States, 585 U.S. ___ (2018) (slip op., at 19, 21)
2.18 U.S.C. § 2703(d); 819 F.3d 880, 884 (6th Cir. 2012).
3. 819 F.3d, at 886.
5. Carpenter, slip op., at 3, 11 n 3.
6. 565 U.S. 400, 404 (2012).
7. 819 F.3d at 884.
8. id., at 885.
9. id., at 885, 890, 893.
10. Carpenter, slip op., at 11,18-19.
11. 389 U.S. 347.
12. Carpenter, slip op., at 5, 12.
13. 389 U.S., at 348, 351.
14. Carpenter, slip op., at 5 (citing Smith v. Maryland, 442 U.S. 735).
15. 565 U.S., at 404.
16. Smith v. Maryland, 442 U.S. 735 (1979).
17. 425 U.S. 435 (1976).
18. Carpenter, slip op., at 7-10.
19. Id., at 10-18.
20. 573 U.S., __ , __ (2014).
21. Carpenter, slip op., at 13.
22. id., at 14.
23. 533 U.S. 27 (2001).
24. Carpenter, slip op., at 14.
25. Carpenter, slip op., at 12-15 (citing Kyllo, 533 U.S., at 36).
26. 425 U.S., at 442.
27. Carpenter, slip op., at 16-17.
28. id., at 15.
29. 573 U.S., at __slip op., at 9)
30. Carpenter, slip op., at 17.
33. id., at 18.
34. id., at 18-19, 21-22
35. 819 F.3d, at 897.
36. Carpenter, slip. op., at 18.
37. id., at 18.
38. id., at 17.
39. id., at 11, n 3.
41. United States v. Skinner, 690 F.3d 772, 774-776 (6th Cir. 2012).
42. 819 F.3d, at 894-895.
43. Carpenter, slip op., at 11 n 3.
44. KENNEDY, J., dissenting (slip op., at 2).
45. Carpenter, slip op., at 18-22.
46. U S. v. Leon, 468 U.S. 897, 905-926 (1984).
47. 819 F.3d, at 894-896 (citing US. v. Leon).