One Warrant, 1,686 Phones: Tower Dumps Go Before the Ninth Circuit

TL;DR: EFF and the ACLU filed an amicus brief on November 3 asking the Ninth Circuit to hold that tower dump warrants are categorically unconstitutional. The case is United States v. Spurlock, built on a Mono County Sheriff’s Office warrant that ordered two telecommunications companies to hand over cell site location information for every device connecting near two highway mile markers on a rural California road, over a six-hour window. It produced records for 1,686 devices, and the defendant says the data fed 90 further warrants. The district court called the sweep a general search and then let the evidence stand anyway on good faith grounds. EFF wants the Ninth Circuit to set good faith aside and answer the constitutional question directly. In August, a federal judge in Mississippi went further and held tower dumps per se unconstitutional, but that ruling binds nobody.

What a Tower Dump Does

A tower dump is a warrant with no suspect attached. Andrew Crocker at the Electronic Frontier Foundation groups the technique with geofence warrants as a “reverse location search,” noting that “Tower dumps are a somewhat older technique than geofence warrants” ^[1]. The Center for Democracy and Technology spells out what that means in practice: collecting location data for every cell phone that “ping off a cell tower (or sets of multiple towers)” ^[2].

The scale is the problem. Ryan T. Fenn and Lee M. Cortes Jr. wrote for the law firm Arnold and Porter that one tower dump search can yield “thousands if not tens of thousands” of records, and that most of them belong to people with no connection to any crime ^[3].

In August, a federal judge in Mississippi spelled out the standard: Carlton Reeves said the government cannot have “access to an entire haystack because it may contain a needle.” He held that tower dump warrants are “per se” unconstitutional ^[3].

Arnold and Porter notes the limits of that win. The ruling binds no other court, may be treated as dictum, and the ex parte posture leaves no clear path to appeal. Officers relying on warrants issued elsewhere can still invoke the good faith exception ^[3].

Two Bodies on a California Highway

United States v. Spurlock starts with a crime scene. Crocker writes that the case “involves an investigation into two murder victims discovered on the side of a rural California highway.” Police “quickly sought a tower dump warrant for an area covering this stretch of road, which eventually revealed location data on nearly 1,700 unique phones” ^[1].

McDermott Will and Schulte, counsel for a separate privacy coalition, supplies the mechanics: the warrant came from the Mono County Sheriff’s Office and directed two telecommunications companies to hand over cell site location information for every device connecting near two rural highway mile markers during a six-hour period. It identified no suspect, no device and no phone number in advance, and produced records for 1,686 devices ^[4].

One warrant, and then the cascade. John Wesley Hall’s Fourth Amendment blog quotes the district court opinion in the case: the search led to roughly 90 further warrants, which the opinion attributes to Spurlock, and those warrants “may have relied at least in part on evidence obtained in response to warrant 20-SW-56” ^[5]. The defendant, Cory Spurlock, is appealing ^[4].

The Court Called It a General Search. Then Let It Stand.

The case came out of the District of Nevada in April 2025. EFF reports that the court relied on an appeals court decision about geofence warrants to hold that tower dumps are similarly categorically unconstitutional “general warrants.” Then it refused to suppress the evidence, putting its weight on the good faith doctrine ^[1].

The reasoning was about novelty, not about privacy. Hall quotes the court: “We cannot fault law enforcement’s actions considering the novelty of the technique and the dearth of court precedent to follow.” The court also noted, in a passage quoting an earlier decision, “This is particularly true in light of the fact that in 2012, no circuit court had yet held the Fourth Amendment applicable to CSLI data” ^[5]. So the data stayed in.

That is the hinge the appellate fight is about. The finding of unconstitutionality survived. The evidence did not.

The Supreme Court has already moved the line on the neighboring technique. On June 29, 2026, in Chatrie v. United States, the Court held that location data revealing a person’s physical movements is protected by the Fourth Amendment even when the surveillance is brief ^[6]. Andrew Crocker and Jennifer Lynch wrote for EFF that the ruling affirmed that app data is subject to the Fourth Amendment because users reasonably view it as their own, and that the Court did not decide whether the particular warrant in Chatrie was reasonable, or whether the good faith doctrine applied ^[6]. Those questions went back down to the Fourth Circuit ^[6].

Two Briefs, One Ask

EFF and the ACLU filed their brief on November 3. The brief’s argument is blunt: “Searching all people in an area without probable cause to believe they were all involved in the criminal activity under investigation reproduces the evils of general warrants and is not constitutionally permitted” ^[1].

EFF also wants the Ninth Circuit to set good faith aside, and says why in one long sentence: “Finally, we argue that the Fourth Amendment requires the court to set aside the good faith doctrine in cases like these and actually decide the constitutional issue. Too often courts pass the buck in cases involving novel surveillance techniques, leading to situations where police can continue using the technique for years or even decades without a definitive ruling” ^[1].

EFF is also asking the court to require strict limits on the scope and duration of these warrants, notice to the people swept up in them, and after-the-fact deletion and minimization of irrelevant data ^[1].

A second group of amici filed its own brief in the case: the Center for Democracy and Technology, joined by Defending Rights and Dissent, the Electronic Privacy Information Center and the Surveillance Technology Oversight Project ^[4]. CDT wants the Ninth Circuit to hold the warrant “an unconstitutional general warrant.” It says the warrant lacked particularity, narrowing mechanisms, and probable cause of wrongdoing, and hopes the court will find the measure fits “precisely the type of general warrant the Founders sought to prohibit” ^[2].

McDermott Will and Schulte, counsel for that coalition, adds the warning: if courts let this stand, the same reasoning could travel to other expansive “reverse” warrants covering location data, search terms, IP addresses and AI prompts ^[4].

Why It Matters

Crocker calls Spurlock “the first such case to be heard by a federal appeals court” since the Supreme Court’s ruling ^[1]. So no federal appeals court has yet applied Chatrie to tower dumps. Our coverage of the geofence fight runs from the Supreme Court ruling, through the argument about every phone near a scene, to the day the Court heard it.

Both answers are already on the record. A federal judge in Mississippi has called tower dumps per se unconstitutional ^[3], while the district court in this case called the sweep a general search and let the evidence stand on good faith ^[1]. The Ninth Circuit now has to say which of those governs. For everyone whose phone showed up in the Spurlock dump, the question was never whether their location data was sensitive. It was whether a court would let it stand. On good faith, it did.

What to Watch

The decision. The ACLU’s case page lists United States v. Spurlock as ongoing before the Ninth Circuit ^[7]. Filing briefs is not a ruling, and the court has not decided the case.

Which question comes first. EFF asks the court to take the categorical constitutional question rather than the good faith question, and warns that courts keep “passing the buck” on novel surveillance techniques ^[1].

The safeguards. EFF asks for limits on warrant scope and duration, notice to the people swept up, and deletion and minimization of data that turned out to be irrelevant ^[1].

Other courts. Reeves’s August decision calls tower dumps per se unconstitutional, but it binds nobody, and officers relying on warrants issued elsewhere can still invoke the good faith exception ^[3].