Imagine you’re cruising down the highway, tunes up, windows down. Suddenly, flashing lights in your rearview. So you pull over, heart racing. The officer approaches and asks for your phone. You refuse to unlock it. Without hesitation, they hold it up to your face. Click. Unlocked. So they start scrolling through your personal messages, photos, and apps. No warrant. No consent. Is this legal? Maybe. But you could have avoided the entire scenario by disabling facial recognition so your phone only unlocks with a passcode.

The thumbprint tug-of-war

In 2014, the U.S. Supreme Court ruled that police need a search warrant to demand your PIN so they can unlock and search your phone–just like any other password. But within years, biometrics threw a wrench in the digital cogs.

Jeremy Travis Payne, a California parolee, was stopped by the CHP in 2021. Officers forced his thumb onto his phone, unlocking it. In United States v. Payne, the Ninth Circuit ruled this didn’t violate the Fifth Amendment because “the compelled use of Payne’s thumb to unlock his phone… required no cognitive exertion.” They likened it to providing a physical key.  

Contrast that with United States v. Brown. In 2025, the D.C. Circuit found that compelling a suspect to use a thumbprint to unlock a phone was not just physical, it was “testimonial.” Thus it violated the Fifth Amendment. The court stated, “Unlocking the cellphone represented the appellant’s thoughts of ‘I know how to open the phone,’ ‘I have control over access to this phone,’ and ‘the print of this specific finger is the password to this phone.’”  

Facial recognition is the new frontier

While the Supreme Court has yet to weigh in on police using our thumbs without a warrant, the phone industry has moved on to facial recognition.

In United States v. Wright, detectives held a phone up to the suspect’s face to unlock it using facial recognition. The court ruled this action violated the Fifth Amendment, stating that biometric unlocking is “functionally the same as a passcode.” They emphasized that using facial recognition to unlock a phone is testimonial because it implies control over the device.  

However, not all courts agree. Some jurisdictions allow law enforcement to compel facial recognition unlocking, viewing it as non-testimonial. The legal landscape is fragmented, with different courts interpreting the use of biometrics in varying ways.

Passcodes vs facial recognition: the legal Wild West

The Supreme Court hasn’t provided clear guidance on whether using biometrics like facial recognition or fingerprints to unlock phones is protected under the Fifth Amendment. This lack of a definitive ruling has led to a patchwork of decisions across the country. Some courts view biometric unlocking as non-testimonial, while others see it as a violation of constitutional rights.

With facial recognition technology becoming more prevalent, the urgency for a unified legal standard grows. Until then, individuals concerned about privacy might consider disabling biometric unlocking features. Relying on a strong passcode could offer better protection against warrantless searches during encounters with law enforcement.

While it’s unclear what individual police departments will choose to do—or can get away with—some courts have ruled on the legality of asking for a passcode or biometric unlocking without a warrant. Here are those rulings, by district and state (according to the New York Law School, updated November 2024).