America’s Smartphone as Ankle Monitor: The Fourth Amendment Crisis of Geofence Warrants

In Chatrie v. United States, currently before the Supreme Court, the petitioner’s attorneys made a striking analogy: geofence warrants have turned the smartphones in Americans’ pockets into “ankle monitors” for the government. “The resulting system of near perfect surveillance is as if the government had ‘attached an ankle monitor’ to tens of millions of Americans,” they argued.

The comparison is provocative—and for those of us who work in the electronic monitoring industry, deeply illuminating. It forces us to confront an uncomfortable question: If warrant-authorized GPS tracking of criminal defendants raises constitutional concerns, what does it mean when the government can access similar location data from hundreds of millions of innocent citizens?

What Geofence Warrants Actually Do

The mechanics are straightforward but sweeping. When investigating a crime, law enforcement serves a warrant on Google (or another tech company) requiring it to:

1. First step: Identify all devices within a specified geographic boundary during a time window—often capturing dozens or hundreds of innocent people
2. Second step: Provide more detailed location histories for selected devices
3. Third step: Unmask the identities of specific users

In the Chatrie case, this process started with 19 phones within 150 meters of a Virginia bank during a robbery, eventually narrowing to three identified individuals—including Okello Chatrie, who was subsequently convicted.

The scale is staggering. Google reported receiving 982 geofence warrant requests in 2018. By 2020, that number had exploded to 11,554—an 1,077% increase in just two years. By 2021, geofence warrants constituted 25% of all U.S. search warrants submitted to Google.

The Ankle Monitor Analogy: More Apt Than It Seems

As industry professionals who design and deploy GPS ankle monitors for criminal justice supervision, we recognize the technical similarities the petitioner’s attorneys highlighted. Both systems:

• Capture precise geolocation data: Modern GPS ankle monitors achieve sub-2-meter accuracy; smartphone location data typically falls within 3-10 meters
• Create continuous movement records: Both generate timestamped location histories that can reconstruct a person’s movements over time
• Enable retrospective surveillance: Both allow authorities to analyze where someone was at any given moment in the past
• Reveal patterns of life: Medical appointments, worship attendance, political meetings, romantic relationships—both technologies expose intensely private information

But here’s where the analogy becomes uncomfortable for civil libertarians and industry professionals alike: ankle monitors operate under far more constitutional scrutiny than smartphone surveillance.

The Constitutional Double Standard

Electronic ankle monitors require:

• Individualized probable cause: A specific person is identified before monitoring begins
• Judicial determination: A judge must find monitoring is appropriate for that specific defendant
• Legal authority: The monitored individual is under court jurisdiction through arrest, conviction, or court order
• Clear purpose: Pretrial supervision, sentence compliance, or victim protection
• Defined duration: Monitoring has a beginning and end tied to legal proceedings

Geofence warrants, by contrast:

• Cast a dragnet first, investigate later: Everyone near a location is swept up, then suspects are identified
• Lack individualized suspicion: The 19 people in the Chatrie geofence were searched simply for being in the wrong place at the wrong time
• Target the innocent: By definition, most people captured in a geofence have no connection to the crime
• Operate in secret: Subjects never know they were searched unless they become suspects

Chief Justice Roberts captured this tension during oral argument, asking whether the government could use geofence warrants “to find out the identities of everybody at a particular church, a particular political organization.”

What the EM Industry Can Teach About Surveillance Standards

The electronic monitoring industry has spent decades developing frameworks for legally and ethically defensible location surveillance. If smartphones truly function as de facto ankle monitors, perhaps these frameworks offer guidance:

1. The Consent Problem

During oral argument, Justice Alito suggested Chatrie had “voluntarily disclosed to Google the information about where he was going to be” by enabling location services. But as the petitioner’s counsel noted, midnight consent checkboxes to “get your phone to work correctly” may not constitute meaningful Fourth Amendment waiver.

In electronic monitoring, consent frameworks are explicit: defendants understand they are being monitored, by whom, and for what purpose. The EFF and ACLU have both argued that even explicit EM consent raises constitutional concerns—making implicit smartphone consent far more problematic.

2. Data Retention and Sharing

The EFF recently filed an amicus brief in Simon v. San Francisco challenging pretrial GPS monitoring programs that indefinitely retain location data and share it with other law enforcement agencies without additional warrants. If such practices raise Fourth Amendment concerns for 125,000 people on ankle monitors, they raise far greater concerns for the 500 million devices Google searches through.

3. Technical Safeguards

Modern electronic monitoring systems incorporate technical privacy protections:

• Encryption standards (AES-128/256)
• Access controls limiting who can view location data
• Audit trails tracking data access
• Automatic data deletion after case closure

Geofence warrant processes have no comparable standardized protections. Once location data is unmasked, it enters law enforcement systems with varying retention policies and access controls.

The Good Faith Exception Controversy

Perhaps the most troubling aspect of the Chatrie case is how it reached the Supreme Court. The district court found the geofence warrant violated the Fourth Amendment—but allowed the evidence anyway under the “good faith exception,” which permits illegally obtained evidence if police reasonably believed their conduct was lawful.

The petitioner argues this creates a catch-22: If courts never suppress evidence from unconstitutional geofence warrants because police acted in “good faith” before clear rules existed, no rules will ever develop. Law enforcement will continue using warrants courts have deemed unconstitutional, immunized from consequences.

For the electronic monitoring industry, this has direct implications. Courts regularly scrutinize EM data and procedures. Defense attorneys challenge GPS evidence based on accuracy, tampering, and chain of custody. If geofence warrant data receives less scrutiny than ankle monitor data—despite affecting vastly more people—something is deeply wrong with our Fourth Amendment framework.

What the Justices Signaled

The April 27, 2026 oral arguments revealed a divided court. Some justices, including Justice Barrett, emphasized that Chatrie was in a “public location” where “nobody has a reasonable expectation of privacy in their public observable movements.” Others, like Justice Gorsuch, worried that ruling for the government would give it “unfettered access” to all cloud-stored data—emails, photos, documents, calendars—without warrants.

Justice Sotomayor suggested a middle ground: requiring warrants that are “particular as to time, place” with explained “reasons why those limitations are reasonable.” This would establish baseline standards without banning geofence warrants entirely.

Deputy Solicitor General Feigin made a practical observation: Google has changed its practices. Location history is now stored on devices themselves rather than Google’s servers, making geofence warrants less effective going forward. But this doesn’t resolve the constitutional questions—or address the other tech companies that may store similar data.

Implications for Electronic Monitoring Policy

The Chatrie case forces a broader reckoning. If the Supreme Court holds that geofence warrants violate the Fourth Amendment, it will establish that mass location surveillance—even with a warrant—requires some form of particularized suspicion before the search begins.

This principle would logically extend to electronic monitoring programs. The EFF has already argued that EM data sharing violates the Fourth Amendment. The ACLU has challenged pretrial monitoring programs that impose “digital incarceration” without adequate due process.

If smartphones-as-ankle-monitors is constitutionally problematic, actual ankle monitors face renewed scrutiny. Agencies deploying GPS supervision may need to:

• Limit data retention periods
• Restrict data sharing between agencies
• Provide clearer notice to monitored individuals
• Implement stronger technical safeguards
• Establish judicial oversight of data access

Conclusion: The Surveillance We Choose vs. The Surveillance We Accept

The ankle monitor comparison in Chatrie cuts both ways. Yes, geofence warrants turn smartphones into surveillance devices with capabilities once reserved for criminal supervision. But it also highlights that electronic monitoring—conducted under court order, with judicial oversight, targeting specific individuals with legal justification—operates under far stricter constitutional constraints than the mass surveillance we’ve all passively accepted.

When the Supreme Court issues its ruling later this year, it won’t just affect criminal investigations. It will define how much location privacy Americans retain in an age when every pocket contains a GPS transmitter streaming data to corporate servers—data the government can access with a warrant that doesn’t name you, doesn’t require suspecting you, and operates entirely without your knowledge.

That’s not an ankle monitor. It’s something potentially more intrusive—and far less regulated.