Biometric privacy on trial: The constitutional stakes in United States v. Brown

In January 2025, the U.S. Court of Appeals for the District of Columbia Circuit issued a ruling that may ultimately reshape the boundaries of constitutional rights in the digital age. In United States v. Brown, the D.C. Circuit held that the FBI violated the Fifth Amendment when it compelled a defendant to unlock his smartphone using his thumbprint.

The court’s reasoning directly challenges how biometric security like fingerprints and facial recognition interacts with self-incrimination protections, igniting a profound legal debate with implications ranging from criminal procedure to immigration enforcement and national security.

The court’s opinion deals with the case of Peter J. Schwartz, a 49-year-old Pennsylvania man who was one of the most heavily sentenced individuals from the January 6, 2021, attack on the U.S. Capitol. Schwartz was convicted of nine felonies and two misdemeanors, including assaulting federal officers with a folding chair and pepper spray.

In 2023, he was sentenced to 170 months in federal prison. During a search of his residence, FBI agents found a cellphone in his bedroom. Schwartz declined to provide a valid numeric passcode, so the agents compelled him to unlock the device using his fingerprint. That act revealed incriminating text messages later used against him in court.

On appeal, Schwartz argued that the act of unlocking the phone with his fingerprint constituted a testimonial act and therefore violated his Fifth Amendment right not to be compelled to be a witness against himself. The D.C. Circuit agreed.

The Fifth Amendment provides that no person “shall be compelled in any criminal case to be a witness against himself.” While courts have long interpreted this to apply to spoken or written confessions, the lines become blurred when physical acts are involved. The Supreme Court has historically drawn a distinction between “testimonial” evidence – communications that reveal the contents of one’s mind -and “non-testimonial” physical evidence like blood samples, handwriting, or fingerprints taken during booking.

The D.C. Circuit, however, concluded that using a fingerprint to unlock a smartphone is not the same as being fingerprinted during arrest. Unlike routine fingerprinting, biometric unlocking communicates information about the individual’s knowledge and control over the device.  The court reasoned that Schwartz’s compliance with the order to use his thumbprint was functionally equivalent to verbally answering a series of questions. In doing so, the compelled act not only confirmed the device belonged to him, but also his exclusive access and knowledge of its contents.

This reasoning places biometric unlocking squarely within the “act of production” doctrine, a legal theory under which the compelled act of producing evidence may itself be testimonial if it communicates assertions of fact. In this view, the fingerprint becomes not just a physical identifier but a silent admission, a key turned by knowledge rather than mere biology.

Just months before Brown, however, the Ninth Circuit Court of Appeals took the opposite view in United States v. Payne. That case involved a parolee compelled to use his fingerprint to unlock a phone. The court held that the act was non-testimonial, likening it to compelled blood draws or handwriting samples – physical procedures not protected by the Fifth Amendment. Relying on precedents like Schmerber v. California and Doe v. United States, the Ninth Circuit emphasized that because the action required no “cognitive exertion,” it didn’t qualify for constitutional protection.

The divergence between the two federal circuit courts has created a classic “circuit split,” a situation that almost inevitably calls for resolution by the U.S. Supreme Court. Legal scholars point out that this split could not be more consequential, as it directly affects how courts across the country treat compelled access to devices that contain vast troves of personal, private, and potentially incriminating information.

What’s at stake in the Brown decision goes far beyond criminal law. In the digital age, smartphones are extensions of the self, containing everything from personal messages and photos to financial records, location data, and even health information. Unlocking one’s device may reveal more than a house search could have in the 18th century, and the very kind of search the Bill of Rights was designed to restrict.

If the D.C. Circuit’s reasoning prevails, biometric security methods like Apple’s Face ID, Samsung’s iris scans, and various fingerprint unlock systems could receive constitutional protection when used to lock private data. That, in turn, could significantly limit law enforcement’s ability to compel access to devices without a warrant or consent.

Moreover, such a ruling would align biometric authentication with established protections for passcodes. Courts have long recognized that requiring a suspect to reveal a memorized passcode is testimonial and therefore protected. If a fingerprint or facial scan is treated differently, the distinction is arbitrary at best, and at worst, dangerously undermines digital privacy.

The implications of Brown are especially acute at the U.S. border. Customs and Border Protection (CBP) officers operate under different legal standards than domestic law enforcement. At the border, agents have broad authority to inspect electronic devices without a warrant under the “border search exception.”

Although CBP cannot legally compel travelers to disclose their passcodes, it has increasingly relied on biometric tools to compel access. CBP agents can detain travelers, seize phones, and pressure individuals – particularly non-citizens – to unlock their devices using their fingerprint or face. This raises troubling questions about coercion and the erosion of constitutional safeguards at ports of entry.

Recent reporting has documented incidents in which attorneys, journalists, and political dissidents were singled out for device searches, often after expressing political opinions critical of the government. If biometric unlocking is testimonial, as the D.C. Circuit holds, then CBP’s routine practices may be unconstitutional, especially when tied to viewpoint-based targeting.

With the legal terrain growing more complex, another question also emerges, which is, could law enforcement simply sidestep the Fifth Amendment by spoofing a fingerprint or face? In theory, yes. But practically it’s far from simple. In 2020, cybersecurity researchers at Cisco Talos published a study showing that spoofing fingerprints could unlock smartphones in about 80 percent of cases. They used high-resolution images or molds of registered users’ prints. However, success varied significantly based on phone model, sensor type, and software version.

Modern devices increasingly incorporate “liveness detection” to ensure the biometric is from a living person. Some models resist spoofing even when the fingerprint mold is perfect. That, combined with regular security updates from phone manufacturers, makes spoofing more of a theoretical workaround than a viable law enforcement strategy. Moreover, even if a spoofed biometric works, it still raises Fourth Amendment concerns. Using someone’s biometric data without consent – especially if acquired during routine booking – could constitute an unreasonable search.

With the D.C. and Ninth Circuits in direct opposition, legal experts expect the Supreme Court to necessarily weigh in. A ruling would resolve not only the immediate conflict, but it would also define how digital-era privacy fits within a centuries-old Constitution.

Some scholars believe the high court may follow the logic of Carpenter v. United States in which the justices ruled that law enforcement needs a warrant to access historical cell site location data. The Court recognized that new technologies necessitate new interpretations of privacy. If that rationale holds, biometric unlocking may soon fall within the protective scope of the Fifth Amendment.

Others, meanwhile, caution that the Roberts Court may tread cautiously, issuing a narrow ruling that depends heavily on context, such as whether the individual is in custody, whether a warrant exists, or whether the device is government property. But the deeper philosophical question remains: Does the Constitution evolve with technology, or does its original meaning rigidly bind modern interpretations?

The D.C. Circuit’s opinion in United States v. Brown represents a pivotal moment in the evolution of constitutional law. By treating biometric unlocking as a testimonial act, the court acknowledges a simple but profound truth, which is that in the digital age one’s body is the key to one’s most private life. When the act of touching your phone becomes indistinguishable from confessing, the Fifth Amendment must keep pace. Whether the Supreme Court agrees though remains to be seen. And until it does, Americans will live in a divided legal landscape.

Article Topics

access control  |  biometrics  |  fingerprint biometrics  |  police  |  smartphones