In Carpenter v. United States, decided June 22, 2018, the Supreme Court held 5–4 that the government's acquisition of historical cell-site location records is a Fourth Amendment search, so police generally need a warrant. The Court called the decision narrow. It left the older rules for bank and phone-company records in place, did not decide real-time tracking or tower dumps, and said subpoenas will still work in the overwhelming majority of investigations.
Key takeaways
- Historical cell-site location information is protected: the Court said people keep a legitimate expectation of privacy in the record of their movements (Carpenter v. United States, 585 U.S. 296).
- The Court held only that accessing seven days of these records is a search. It did not set a shorter safe zone.
- Expressly left open: real-time tracking, tower dumps, security cameras, business records that incidentally reveal location, and national security collection.
- Subscriber details, call logs and many other records still move on subpoenas, including DEA administrative subpoenas under 21 U.S.C. § 876 that no judge signs.
- Winning a Carpenter argument doesn't guarantee suppression. On remand, Carpenter's own conviction stood under the good-faith exception (Sixth Circuit, June 11, 2019).
01What cell-site location records are
A phone checks in with nearby cell towers constantly. Each connection creates a time-stamped record of which tower and which sector handled it. Carriers keep these records for business purposes. Lawyers call them cell-site location information, or CSLI.
One record says little. Months of them can trace where a person sleeps, works, worships and spends the night. That is the core of the Court's reasoning: the records are detailed, comprehensive and collected without the user doing anything except carrying a phone.
This is different from device-based tracking with a cell-site simulator, where police imitate a tower to locate a phone directly. We cover that in What Is a StingRay?
02The case: 127 days, 12,898 points
After a string of armed robberies at RadioShack and T-Mobile stores in Michigan and Ohio, police arrested four men. One of them identified accomplices and gave investigators their phone numbers.
Prosecutors then got court orders under the Stored Communications Act, 18 U.S.C. § 2703(d). That statute lets a judge order records if the government offers "specific and articulable facts" showing reasonable grounds to believe they are relevant to an investigation. That is far below probable cause, the standard for a warrant.
The carriers produced 127 days of records from one and two days from another. In all, the government obtained 12,898 location points for Timothy Carpenter, about 101 a day. He was convicted on robbery and firearm counts and sentenced to more than 100 years in prison (Carpenter v. United States, 585 U.S. 296).
03The third-party doctrine it narrowed
The government's argument rested on the third-party doctrine: the rule that you lose Fourth Amendment protection for information you voluntarily hand to a business.
- United States v. Miller, 425 U.S. 435 (1976) held that bank records subpoenaed from a bank were the bank's business records, not the customer's private papers.
- Smith v. Maryland, 442 U.S. 735 (1979) held that a pen register, a device recording the numbers dialed from a phone, was not a search. The Court said people have no legitimate expectation of privacy in information they voluntarily turn over to third parties.
In Carpenter, Chief Justice Roberts, joined by Justices Ginsburg, Breyer, Sotomayor and Kagan, declined to extend those cases. The majority said Smith and Miller also turned on the limited nature of the records involved. Location history has no such limits, and users don't meaningfully share it in the ordinary sense. Justices Kennedy, Thomas, Alito and Gorsuch dissented.
04What the Court held, and the seven-day line
The holding: acquiring historical CSLI is a search, and the government generally must get a warrant supported by probable cause first. A § 2703(d) order doesn't meet that standard.
The opinion's footnote 3 drew the line people now cite. The Court did not decide whether police could get a shorter period of location records without Fourth Amendment scrutiny. It held only that accessing seven days of CSLI is a search. Carpenter's own case involved far more.
The Court also kept the usual exceptions. Exigent circumstances (an emergency such as a fleeing suspect, a threat of imminent harm or the risk that evidence will be destroyed) can still justify warrantless access. The opinion said it does not limit police responses to urgent situations such as bomb threats, active shootings or child abductions.
It doesn't say fewer than seven days is fair game. It says the question wasn't decided. Anyone claiming a bright "under seven days, no warrant" rule is reading more into the opinion than it holds.
05What Carpenter expressly left open
The majority called its decision "a narrow one" and listed what it was not deciding:
- Real-time CSLI: location data collected going forward rather than from stored history.
- Tower dumps: a download of every device that connected to a particular tower during a window of time.
- Smith and Miller themselves, which still stand.
- Conventional surveillance tools, such as security cameras.
- Other business records that might incidentally reveal location.
- Collection involving foreign affairs or national security.
And one sentence that matters as much as the holding: the government "will be able to use subpoenas to acquire records in the overwhelming majority of investigations." A warrant is needed only in the rare case where a suspect has a legitimate privacy interest in records a third party holds (Carpenter v. United States, 585 U.S. 296).
Lower courts have been working through these open questions since. We haven't compiled how each circuit has ruled, and we won't summarize what courts "all" hold without a source that does.
06What still flows without a warrant
Here is where the line sits for common record types, based on the opinion and the statutes it discusses.
| Record | Typical legal process | After Carpenter |
|---|---|---|
| Historical CSLI | Was a § 2703(d) order | Warrant generally required (seven days or more held to be a search) |
| Numbers dialed | Pen register or subpoena | Smith left in place |
| Bank records | Subpoena | Miller left in place |
| Real-time location, tower dumps | Varies | Not decided |
For drug investigations, the subpoena is often administrative. Under 21 U.S.C. § 876, the Attorney General can subpoena records the government finds "relevant or material to the investigation." The statute's text doesn't require a judge's approval to issue one; a court gets involved only if someone refuses to comply.
That authority has supported bulk programs. USA Today, Apr. 7, 2015 reported that from 1992 until 2013, the DEA used administrative subpoenas to collect logs of billions of calls from the U.S. to as many as 116 countries. And Sen. Wyden's Wyden letter, Nov. 20, 2023 describes the Hemisphere call-records service operating on subpoenas in most states, with a capability to obtain location data.
Whether any location data produced through Hemisphere or similar services would require a warrant under Carpenter isn't answered by the public record. It depends on what the data is and how it was obtained, which is exactly the information these programs keep out of reports.
07How defendants raise Carpenter
The usual vehicle is a motion to suppress: a request asking the judge to exclude evidence obtained in violation of the Constitution. A defendant has to know the records exist and how they were obtained before filing one.
Winning the constitutional argument isn't the end. When the Supreme Court sent Carpenter's case back, the Sixth Circuit agreed the warrantless collection violated the Fourth Amendment but still refused to suppress. It applied the good-faith exception, which spares evidence when officers reasonably relied on a statute later found inadequate, citing Illinois v. Krull (Sixth Circuit, June 11, 2019). Carpenter's conviction stood.
Questions a defendant can raise with a lawyer:
- What location records exist in the case, for how many days, and were they historical or real-time?
- What legal process produced them: a warrant, a § 2703(d) order, a subpoena or an emergency request? On what date?
- Was a tower dump or area-wide request used to identify a phone in the first place?
- Did any records come from an administrative subpoena or a records service that doesn't appear in the reports?
- If a records request preceded the first documented step of the investigation, is it in discovery? See Section 702 backdoor searches for the national security version of this question.
08FAQ
Do police always need a warrant for phone location data?
Not always. Carpenter held that acquiring historical cell-site location records is a search that generally requires a warrant, but exceptions such as exigent circumstances still apply, and the Court did not decide real-time tracking or tower dumps.
Is there a rule that fewer than seven days of location data needs no warrant?
No. The Court held that seven days is a search and expressly declined to decide whether a shorter period could be obtained without Fourth Amendment scrutiny.
Does Carpenter protect call logs and subscriber information?
Carpenter left Smith v. Maryland and United States v. Miller in place and said subpoenas will still work in the overwhelming majority of investigations. Records like numbers dialed generally remain outside its holding.
If police got location records without a warrant, will the evidence be thrown out?
Not automatically. On remand in Carpenter's own case, the Sixth Circuit found a Fourth Amendment violation but applied the good-faith exception because agents relied on the Stored Communications Act, so the evidence stayed in.
Does Carpenter apply to national security surveillance?
The Court said its decision did not consider collection techniques involving foreign affairs or national security. That question was left open.
Know a case where the location records came from nowhere?
Send us the court, the docket number and any suppression filings. We work from public records and correct our own work. If you are the person charged, talk to your own lawyer before sharing anything about your case with anyone, including us. Messages to us are not privileged.
09Sources
Every fact in this dispatch comes from the documents below. If you spot an error, tell us and we'll correct it on this page.
- Carpenter v. United States, No. 16-402, 585 U.S. 296, June 22, 2018, Cornell LII
- Smith v. Maryland, 442 U.S. 735, 1979, Cornell LII
- United States v. Miller, 425 U.S. 435, 1976, Cornell LII
- 18 U.S.C. § 2703 (Stored Communications Act), Cornell LII
- 21 U.S.C. § 876 (administrative subpoenas), Cornell LII
- United States v. Carpenter, No. 14-1572 (6th Cir.), opinion on remand, June 11, 2019
- USA Today, DEA bulk telephone records operation, Apr. 7, 2015
- Sen. Ron Wyden, letter to Attorney General Merrick Garland on Hemisphere, Nov. 20, 2023
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Public education, not legal advice. We are not attorneys. If you are facing charges, talk to your lawyer before sharing anything about your case with anyone, including us.