Most people use Face ID or a fingerprint to unlock their phones because it’s fast and convenient. But there’s a legal loophole that doesn’t get talked about enough—and it’s the reason I personally avoid using biometrics as my primary lock method.

Under the Fifth Amendment, you have the right to avoid self‑incrimination. That protection generally covers things you know—like your passcode. But courts have repeatedly ruled that biometrics (your face, your fingerprint, your thumbprint) are not “knowledge.” They’re considered physical characteristics, similar to providing a DNA sample or a fingerprint card.

In many situations, law enforcement can compel you to unlock your phone with your face or fingerprint, even when they cannot legally force you to reveal your passcode.This isn’t about hiding anything—it’s about understanding your rights and how technology interacts with the law. Our phones contain our entire digital lives: messages, photos, financial apps, authentication tools, health data, and more. The legal system simply hasn’t caught up with how much personal information we carry in our pockets.

If you want the strongest legal protection for your device, a passcode is still the safest option. Biometrics are convenient, but convenience sometimes comes with trade-offs we don’t think about until it’s too late.