Forced Phone Fingerprint Swipes Raise Fifth Amendment Questions

A case in California involving blackmail threats made over Facebook Messenger shows how courts are grappling with the constitutionality of requiring fingerprint swipes to unlock smart devices.

A federal judge earlier this year barred Oakland, Calif., police from forcing the alleged blackmailers to swipe open their phones because it was akin to providing potentially incriminating testimony. Police were probing a complaint that two people were threatening to release embarrassing videos of a third person if they didn’t get money.

But around the country, judges have split on whether forcing criminal suspects to open their phones with biometric identifiers, such as ...