Face recognition is still rather gimmicky and unreliable. Finger print scanners on devices are also not that reliable.
In any case, at least in US, your privacy can be invaded by law enforcement if you are relying on a biometric protection like fingerprint.
As per a recent court ruling there, law enforcement cannot force you to unlock or reveal password for a password protected phone because of their 5th amendment rights that protects them from divulging information like passwords that can potentially result in self incrimination. But biometric methods are not protected. So for a device protected by a biometric mechanism like fingerprints, law enforcement can legally ask you to unlock the device though the corresponding biometric.
