When a Touchscreen Becomes Testimony - the 5th Amendment Today

The Fifth Amendment’s Digital Identity Crisis

Consider two people stopped in separate traffic stops under identical circumstances. Both have encrypted smartphones on the passenger seat—devices holding personal messages, financial records, photographs, location history, and the ordinary record of a private life.

The first person protects the phone with a memorized passcode. Courts have generally treated compelled disclosure of such a code differently because revealing it requires disclosure of knowledge residing in the person’s mind—although courts disagree about when the government may invoke a “foregone conclusion” exception.

The second person protects an identical phone with a fingerprint. Some courts have allowed police to use that biometric to open the device, treating a fingerprint as physical evidence—like a blood sample or an ink print.

But the physical-evidence analogy becomes strained when a biometric identifier is used not merely to identify a person, but to open an encrypted digital archive. A fingerprint on a glass identifies a body. A fingerprint used to unlock a phone may communicate that the person has the practical ability to access a vast store of private information.

Chief Justice John Roberts observed in Riley v. California that cellphones are so pervasive that a visitor from Mars might regard them as an “important feature of human anatomy.” The Fifth Amendment question is whether the government may force a person to use that feature as the key to a search of their digital life.

The Fifth Amendment contains protections concerning grand-jury indictments, double jeopardy, self-incrimination, due process, and compensation for government takings. This essay concerns the clause most Americans know as “taking the Fifth”: no person may be compelled in a criminal case to be a witness against themselves.

A constitutional line

The privilege against self-incrimination grew out of resistance to coercive official questioning. In institutions such as the English Star Chamber, a suspect could be compelled to answer incriminating questions under oath. The person faced a cruel choice: confess, lie under oath, or refuse to answer and face punishment for contempt.

The American constitutional answer was not that government could never investigate crime or gather evidence. It was that government should build its case through its own independent work, rather than force the person it seeks to prosecute to supply incriminating testimony.

In Boyd v. United States in 1886, the Supreme Court took a broad view of the connection among compelled papers, privacy, and the Fourth and Fifth Amendments. The Court described constitutional protections against official intrusion as safeguarding “the sanctity of a man’s home and the privacies of life."

Over the twentieth century, however, the Court drew a sharper distinction between compelled testimony and physical evidence. In Schmerber v. California in 1966, the Court held that a compelled blood draw didn't violate the Self-Incrimination Clause because blood was physical evidence, not compelled testimony. That distinction generally places fingerprints, voice exemplars, handwriting samples, and lineups outside the Fifth Amendment privilege—though their collection may still be limited by the Fourth Amendment, due process, statutes, and other rules.

When a body part becomes a key

A smartphone puts pressure on the Schmerber distinction.

A fingerprint is physical. But compelling someone to use that fingerprint to unlock a phone may communicate facts the government doesn't otherwise know. A successful unlock may show that the device recognizes the person’s biometric as authorized and that the person has the practical ability to access it.

Those facts can support an inference of knowledge or control. The unlock alone does not prove device ownership, authorship of messages, or the authenticity of every item investigators later find. But it can establish a consequential connection between a person and an encrypted repository of intensely private information.

That is why the question is not simply “fingerprint versus passcode.” The question is whether the government may compel a person to transform a physical trait into an authenticated access key.

The Fourth Amendment and Fifth Amendment do different work here. The Fourth Amendment asks whether the government may lawfully search a phone’s contents. The Fifth Amendment asks a different question: whether the government may compel the person to perform the potentially testimonial act that makes those contents accessible.

The courts divide

Two federal circuits have now taken materially different approaches to compelled biometric unlocking.

In United States v. Payne, decided in 2024, the Ninth Circuit held that officers’ forced use of a handcuffed parolee’s thumb to unlock a phone he had already identified was non-testimonial. The court accepted that Payne’s thumbprint was compelled and that access to the phone could be incriminating. But it concluded that Payne supplied no “cognitive exertion”: officers used his thumb as physical evidence, analogous to a blood draw or booking fingerprint, to gain access to a possible source of information.

In United States v. Brown in 2025, the D.C. Circuit took a different approach in the case of co-defendant Peter Schwartz. The court held that compelling Schwartz to unlock his phone with his thumbprint was testimonial because the successful act communicated, in substance, that he knew how to open the phone, had access to and control over it, and that his thumbprint was authorized to unlock it.

The difference isn't semantic. In Payne, the compelled use of the thumb in those particular circumstances was treated as a non-testimonial physical act. In Brown, compelling Schwartz to perform the unlock was treated as a communication of knowledge, access, and control.

The Supreme Court hasn't yet resolved this conflict.

The unknown archive

The issue becomes more consequential when prosecutors invoke the “foregone conclusion” doctrine associated with Fisher v. United States. Fisher involved identified accountant work papers. Its basic principle is that compelling production of known materials may not be testimonial if the government can already establish, with sufficient particularity, that the specific materials exist and that the person possesses or controls them.

Applying that rationale to a smartphone raises a different problem. The government may know that a person possesses a device. That is not the same as knowing what it contains, which accounts it opens, what cloud information it can reach, or what evidence it may reveal.

In United States v. Hubbell, the Supreme Court warned that the Fifth Amendment may apply when a government demand forces a person to use “the contents of his own mind” to identify, locate, and assemble evidence for investigators.

Compelled unlocking can raise the same concern. It may amount not to surrendering a known document, but to providing entry into an unknown—and continually changing—digital archive. The government may be relying on the target’s knowledge and cooperation rather than independently identifying the evidence it seeks.

A modern phone is not a single paper file. It may contain years of location information, health data, photographs, communications, financial records, cloud-linked accounts, and the associations that make up a private life. That does not exempt a phone from lawful investigation. It does, however, make the method of gaining entry constitutionally significant.

Silence in the digital age

The Fifth Amendment doesn't forbid law enforcement from investigating crime. It doesn't prevent warrants, lawful searches, or the collection of physical evidence.

It does, however, limit the government’s power to compel a person to become a witness against themselves.

In Riley, the Supreme Court recognized that modern cellphones differ fundamentally from traditional physical objects in both the quantity and quality of information they contain. It held that police generally need a warrant to search digital information on a phone seized incident to arrest.

A fingerprint is physical. But forcing someone to use it as the authenticated key to an encrypted phone may communicate knowledge, access, and control—the kind of testimonial assistance the Fifth Amendment was designed to keep government from extracting by force.

The question isn't whether the government may search lawfully. It's whether the government may make the person it seeks to investigate perform the act that opens the search.