Samsung's newly introduced Galaxy S8 features iris scanning and facial recognition via the front-facing camera. Both these features can be used to unlock the phone for those times when you don't feel like reaching your finger around the back and feeling for its built-in fingerprint reader alongside the rear camera. iDeviceHelp posted a hands-on video with Galaxy S8's biometrics.
They concluded that eyeballs and faces are not as secure as fingerprints because the phone could be tricked into unlocking by scanning a user's headshot.