Bloomberg:

If a person has enabled Apple’s Touch ID, her fingerprint will unlock the phone for 48 hours after locking before the device requires a PIN. Systems on newish Samsung and LG phones work similarly. Los Angeles and Oakland are among the cities that have already granted or received warrants for the use of a finger to unlock a phone. The next step may be a lawsuit that determines whether a fingerprint is off-limits.

Legal scholars say law enforcement is likely to win that fight. Two years ago, David Baust, a paramedic in Virginia Beach, Va., admitted that his locked iPhone 5S may have filmed him in bed strangling his girlfriend, according to a court filing. Baust’s lawyers argued that unlocking the phone would violate his Fifth Amendment right to avoid incriminating himself. A state judge ruled that demanding Baust type in his pass code would entail a “mental process” leading to self-incrimination, but that asking for his fingerprint was more like drawing a blood sample and therefore OK.

As I’ve said in the past, I expect that law enforcement will eventually build a mechanism to pull a fingerprint from a suspect and use that to unlock a suspect’s phone. This concept has been proven and fingerprinting is already widely accepted.