The Canvassing Cell-Site Simulator
and the Fourth Amendment's Hard Stop

On June 22, 2026, U.S. Magistrate Judge Carmen E. Henderson of the Northern District of Ohio issued a written order doing something federal courts almost never do publicly: she said no. The government had applied for a warrant to deploy a canvassing cell-site simulator for 30 days in an Akron criminal investigation. Judge Henderson denied it — and explained exactly why.

The seven-page opinion in In the Matter of the Use of a Canvassing Cell-Site Simulator to Identify a Target Cellular Device, No. 4:26-mj-06151 (N.D. Ohio 2026), is one of the clearest judicial statements yet on where the Fourth Amendment draws the line between targeted digital investigation and unconstitutional dragnet surveillance.

Two Kinds of Cell-Site Simulators

Not all cell-site simulators work the same way, and the distinction matters legally.

A locating CSS tracks a known device — you have the target's phone identifier and you're using the simulator to find where it is. Courts have generally been more comfortable with this use, because the search is already cabined to a specific person and device.

A canvassing CSS is different in kind. It doesn't locate a known device — it sweeps an area to identify which devices are present. The simulator sends a signal; every phone in range responds with its IMSI (International Mobile Subscriber Identity). Investigators then compare IMSIs across multiple locations and times to identify the target by process of elimination.

And here is what makes the IMSI especially powerful: it is not truly anonymous. A single subpoena to the carrier converts an IMSI into a name, address, and phone number. As Judge Henderson noted in footnote 1 of her opinion, the canvassing CSS doesn't just identify a device — it opens a direct pipeline to the subscriber's identity.

What the Government Asked For

The June 15, 2026 warrant application sought authority to deploy the canvassing CSS for up to 30 days, 24 hours a day, at five locations in the Akron area — wherever officers had "reason to believe" the suspect was present. Those five locations included the suspect's residence, overnight location, daytime location, and two heavily frequented spots near a university, a hospital, and commercial areas.

The government did offer some safeguards: it said it would not take investigative steps on collected IMSIs until it had confirmed the target's device across multiple locations, and that it would delete non-target data after identification. Judge Henderson found that insufficient.

Why She Said No: Particularity

Critically, Judge Henderson found that probable cause was not the problem. She said so explicitly. The affidavit established probable cause to believe the suspect was using unknown cellular devices in criminal activity and that identifying those devices would produce more evidence.

The fatal defect was particularity — the Fourth Amendment's requirement that warrants particularly describe the place to be searched and the things to be seized. The government's application failed it on every dimension:

Without those constraints, the warrant would have given investigators access to the IMSI data of thousands of uninvolved, unsuspecting individuals in densely populated areas — people near the university, the hospital, the shops and restaurants — who have no connection to the investigation whatsoever.

She borrowed the decisive analogy from In re Warrant Application for Use of Canvassing Cell-Site Simulator, 654 F. Supp. 3d 694 (N.D. Ill. 2023), a case she cites directly: approving this warrant would be like authorizing a search of an entire apartment building — or an entire city block — when you have probable cause only for one specific unit. And doing it for a month.

The Fourth Amendment’s particularity requirement, she held, “bars this sort of ‘rummaging’ through the proverbial home.”

Beyond One Warrant: The Order’s Broader Significance

Written denials of CSS warrant applications are rare. Most are either granted without published opinion or handled in sealed proceedings. When a federal magistrate issues a reasoned, written denial and it becomes public, it functions as a roadmap — both for courts evaluating future applications and for investigators who need to understand what the Fourth Amendment actually requires.

The opinion situates itself squarely within the emerging digital surveillance doctrine that flows from Carpenter v. United States, 585 U.S. 296 (2018). As Henderson quotes Carpenter — which in turn quoted Justice Brandeis's dissent in Olmstead v. United States — the Court is obligated, as “subtler and more far-reaching means of invading privacy have become available to the Government,” to ensure that “the progress of science” does not erode Fourth Amendment protections. The government’s constitutional obligations do not shrink because the technology advances.

Henderson also cites Judge Gregory’s solo dissent in United States v. Chatrie, 136 F.4th 100 (4th Cir. 2025) (Gregory, J., dissenting), cert. granted sub nom. Chatrie v. United States, No. 25-112 (U.S. Jan. 16, 2026): “The people’s rights against unreasonable searches and seizures cannot bend to accommodate the volatility of technology. Rather, new technologies must bend to accomplish the vitality of the protections guaranteed to the people under the Fourth Amendment.”

The Chatrie Connection

That citation to Chatrie is not incidental. The Supreme Court heard oral argument in Chatrie v. United States, No. 25-112, on April 27, 2026, and a decision is expected before the end of the current term — meaning it could arrive at any time. The question before the Court: whether law enforcement’s use of a geofence warrant to sweep location data from everyone within a defined area violated the Fourth Amendment.

The procedural history matters. The district court found the warrant constitutionally defective but declined to suppress the evidence under the good-faith exception. The en banc Fourth Circuit — in a one-sentence per curiam opinion accompanied by nine separate concurrences and dissents spanning 126 pages — affirmed the denial of suppression, also on good-faith grounds, without resolving the underlying constitutional question. The court was evenly divided, 7–7, on whether a search had even occurred. Only Judge Gregory squarely held, in dissent, that the warrant was unconstitutional and that suppression was required. It is his reasoning that Henderson draws into the canvassing CSS context.

The structural parallel between geofence warrants and canvassing CSS applications is direct. In Chatrie, Google responded to the warrant through a three-step process: first, anonymized location data for all accounts within the geofence; second, expanded location data for a narrowed subset; third, full subscriber identification for a final group — all authorized by a single warrant with no intervening judicial review between steps. A canvassing CSS application asks a court to authorize law enforcement to collect equivalent information directly, without any carrier intermediary, and simultaneously rather than sequentially. Both involve indiscriminate, area-based digital sweeps. Both capture the innocent alongside the guilty. Both require a court to determine whether the Fourth Amendment’s particularity requirement can be satisfied when you do not know — and cannot know — whose data you are capturing until after you have captured it.

The framework the Supreme Court uses to resolve Chatrie will almost certainly shape how courts evaluate canvassing CSS warrant applications going forward. If the Court holds that geofence warrants implicate the Fourth Amendment and must satisfy particularity, that reasoning translates directly to the CSS context. If the Court finds the third-party doctrine controls, the canvassing CSS question becomes harder — but Henderson’s order demonstrates that particularity remains an independent and potent barrier even when probable cause is established. The webinar below will address the decision in full, whatever the outcome.

What Law Enforcement Agencies Need to Know Now

The Henderson order is not a prohibition on canvassing CSS use. It is a specification of what a constitutionally compliant application requires. Agencies and prosecutors who take the time to draft warrants that define geographic parameters, estimate population impact, build in genuine minimization protocols, and limit deployment to locations where the particularity standard can actually be satisfied will be on much stronger ground — both in the courthouse and in the community. The Supreme Court’s forthcoming decision in Chatrie will add another layer of clarity. The agencies that are prepared for both will be the ones that stay ahead of it.