To prevent accidential unlock in a pocket or when sliding to the pocket or when carrying the phone in hand, the fingerprint unlock should have haptic feedback.
Current behaviour: Vibrates twice when incorrect finger is applied, but no haptic feedback when applying the right finger. This results in acceidential unlocks being unnoticed by the user.
Suggested behaviour: Vibrates once when the finger is recognized, vibrates twice when the finger is not recognized.
This idea is taken from my old LG G7.