United States v. Hammond
A Seventh Circuit decision holding that several hours of warrantless, real-time cell-site location tracking on public roads did not constitute a Fourth Amendment search.
Executive Summary
During a three-week series of armed store robberies in Indiana and Michigan, investigators identified Rex Hammond as the likely offender and obtained his cellphone carrier’s assistance under 18 U.S.C. § 2702. The carrier generated real-time cell-site location information that officers used for several hours to follow Hammond’s movements on public roads and arrest him before another suspected robbery. Hammond argued that Carpenter required a probable-cause warrant. The Seventh Circuit disagreed. It treated the short-duration, prospective tracking as more like the beeper monitoring in United States v. Knotts than the 127-day retrospective location history in Carpenter. Because the data revealed only Hammond’s movement on public roads over several hours and did not expose entry into a home or another protected place, the court held there was no Fourth Amendment search. It also concluded that exigent circumstances and good-faith reliance on § 2702 independently defeated suppression.
Key Holdings at a Glance
The Armed-Robbery Investigation
Hammond committed or attempted seven armed store robberies over approximately three weeks. Investigators developed evidence connecting him and his vehicle to the offenses and believed he was preparing to strike again.
Rather than request historical movement records, officers asked the carrier for current location assistance. The carrier’s information allowed them to monitor Hammond’s movement for a matter of hours, converge on his location, and arrest him on a public roadway.
What Real-Time CSLI Revealed
Cellphones regularly communicate with nearby cellular infrastructure. Real-time CSLI uses current network interactions to estimate where a phone is located as the investigation unfolds. Depending on the provider and method, precision can vary significantly.
In Hammond, the information functioned as a prospective tracking aid. It did not allow officers to reconstruct months of past movement or create the comprehensive retrospective archive that concerned the Supreme Court in Carpenter.
Why Carpenter Did Not Control
Carpenter involved seven days of historical CSLI and emphasized the government’s ability to travel backward in time through a deeply revealing record of a person’s movements. The Hammond court stressed that Carpenter expressly described its holding as narrow.
Real-time tracking lacks the same retrospective quality. Hammond’s monitoring also lasted only several hours, produced a limited journey, and did not expose an extended pattern of associations, routines, or private-life details.
The Comparison to United States v. Knotts
In Knotts, officers used a beeper to follow a container during a single automobile journey on public roads. The Supreme Court held that a person has no reasonable expectation of privacy in movements exposed to public observation.
The Seventh Circuit viewed Hammond’s several-hour trip as closer to Knotts than Carpenter. The technology improved officers’ efficiency, but on the facts before the court it did not reveal a comprehensive chronicle or penetrate a private interior.
Duration, Aggregation, and the Mosaic Problem
Hammond does not create a universal rule that all real-time CSLI is outside the Fourth Amendment. The court repeatedly tied its conclusion to several hours of monitoring. Longer or more comprehensive surveillance can reveal patterns unavailable through ordinary visual observation.
As duration grows, location data may expose medical visits, religious practice, intimate relationships, political activity, and other sensitive associations. Agencies should therefore avoid treating the phrase “real time” as a substitute for a probable-cause assessment.
Alternative Holding: Exigent Circumstances
The court concluded that exigency would justify the tracking even if it were a search. Investigators confronted a recent sequence of armed robberies, evidence of an escalating pattern, and a reasonable belief that Hammond posed an imminent danger and might commit another offense.
Exigency depends on facts known when officers act. It should be documented contemporaneously: the threatened harm, why delay creates risk, why the requested data can mitigate that risk, and when the emergency ends.
Alternative Holding: Statutory Good Faith
Section 2702 permits a provider to disclose certain customer information when it believes in good faith that an emergency involving danger of death or serious physical injury requires disclosure without delay. Investigators relied on that emergency process.
The Seventh Circuit held that suppression was independently inappropriate because officers acted in objectively reasonable reliance on the statutory framework. That analysis does not protect fabricated emergencies or requests exceeding the information necessary to address the danger.
What Hammond Does—and Does Not—Establish
- It concerns several hours of real-time CSLI, not prolonged continuous tracking.
- It concerns movement on public roads, not location inside a home.
- It does not overrule Carpenter’s warrant requirement for qualifying historical CSLI.
- It does not hold that every form of prospective phone location is identical.
- It does not eliminate stricter state constitutional or statutory protections.
- It does not make emergency requests a substitute for warrants in routine investigations.
Hammond Compared with Leading Location Cases
| Case | Location Evidence | Central Rule |
|---|---|---|
| United States v. Knotts | Beeper during one public-road journey | No search for short-term public movement. |
| Carpenter v. United States | At least seven days of historical CSLI | Government acquisition generally requires a warrant. |
| United States v. Hammond | Several hours of real-time CSLI on public roads | No search on these facts; exigency and good faith also applied. |
| United States v. Gibson | Ninety days of precise prospective GPS | Judicial orders satisfied warrant requirements. |
Agency Operations Checklist
- Identify the precise location technology and provider process requested.
- Determine whether the data is historical, prospective, or both.
- Use a probable-cause warrant when feasible, especially for precise, prolonged, or private-place tracking.
- For emergencies, document the immediate danger and why delay is unsafe.
- Limit the request to the shortest duration and least data necessary.
- Stop emergency tracking when the threat ends and obtain judicial authority for continued monitoring.
- Preserve requests, provider responses, location points, maps, access logs, dispatch records, and the emergency chronology.
- Check state constitutions, statutes, provider requirements, and current circuit law.
Litigation and Review Checklist
- Determine exactly what data was generated and how.
- Measure the duration, frequency, precision, and geographic reach.
- Identify whether any point disclosed presence in a home or protected location.
- Compare the investigation with Knotts, Carpenter, and controlling state authority.
- Separate the no-search holding from exigency and good-faith alternatives.
- Test whether the emergency was objectively supported when the request was made.
- Determine when the emergency ended and whether tracking continued.
- Analyze derivative evidence and later warrants independently.
Frequently Asked Questions
Did Hammond hold that real-time CSLI is never a search?
No. Its holding is tied to several hours of tracking on public roads without intrusion into a protected place.
Why was Carpenter different?
Carpenter involved a retrospective archive covering at least seven days, while Hammond involved prospective tracking for several hours.
Did officers obtain a warrant?
No. They used the emergency-disclosure process under § 2702.
Was there an emergency?
The court found an objectively reasonable threat of another armed robbery and danger to the public.
Should agencies seek warrants after Hammond?
Yes, when feasible. A warrant provides the strongest protection for precise, prolonged, contested, or private-place location tracking.
Primary Authorities and Related Law
Published appellate opinion addressing several hours of real-time CSLI tracking.
Read the complete opinion
Supreme Court decision protecting qualifying historical CSLI.
Read Carpenter v. United States
Public-road beeper monitoring during a discrete journey.
Read United States v. Knotts
Stored Communications Act provisions governing voluntary provider disclosure, including emergencies.
Read 18 U.S.C. § 2702
Final Assessment
United States v. Hammond occupies the space between a single public journey and a comprehensive digital location history. The court treated several hours of prospective public-road tracking as limited and nonintrusive, while leaving open harder questions involving longer duration, greater precision, protected places, or richer aggregated patterns.