You are warned that face recognition is less secure. This goes with most other manufacturers apart from Apple that use a specific system
@ghostsssss: Face Recognition is a convenient way to unlock your device, but as referenced by @Glenntech it is not considered to be a secure option. If you're worried about the security of your device, which is understandable, then I recommend heading to Settings > Lock Screen > Screen Lock Type, and utilising a Medium or High option such as a Password or PIN. You can also register your fingerprints for added security, and toggle it on as a biometric security option.
