One of the characteristics of Face ID since its inception has been that it is one-person, that is, a single person can unlock the iPhone X, the only currently supported device, and no one else. At the moment users can only register one face on the iPhone to unlock it, although many have tried to get around this restriction using unofficial methods.
iOS 12 adds a new option to Face ID settings that allows you to register an "alternate appearance", not a second face, despite what many blogs are trying to publish. We explain how this new iOS 12 option works.
We have the new option within the Settings menu of iOS 12, in "Face ID and code> Set up an alternate look". As you can read just below, there is no mention of adding another face, just that, an alternative look.
In addition to continuously recording your appearance, Face ID can recognize an alternate appearance
Remember that Face ID works by continuously learning and registering new facial characteristics so that its reliability is greater and greater. Recording an alternate appearance can be useful for users who have very different appearances throughout the day, such as workers who wear hard hats or goggles, or people with long hair whose appearance can look radically different according to the hairstyle that is carried out. These are just two examples of when this new ability to record a "second appearance" can be useful.
Nowhere does it say that a second face can be used to unlock the device, and using it for that can have important consequences at the security level, since the system may not be as reliable as it should be. It is also convenient to remember that Face ID is not only used to unlock the device, but to make purchases in applications, on web pages or even to pay with a credit card, so that everyone is responsible for their actions.