During the first demonstration of Face ID by Craig Federighi at presentation iPhone X, there was a small blunder. The reason for this was not a malfunction of the new authentication technology, but rather its design.
Apple explained what happened:
'The employees had taken their smartphone to the stage beforehand and did not notice that Face ID was trying to identify their face. Since this was not Craig's face, there were several errors and iPhone did what he had to – asked for the password. In other words, Face ID worked exactly as it should. '
You yourself can reverse engineer this situation with Touch ID. Just press the sensor with an unregistered finger several times, and after five attempts iPhone it will ask for a password. The same thing happened with Face ID.
But the mistake happened anyway. Yes, Face ID worked as it should, but this incident spoiled the impression of the presentation.