The Face ID is a facial recognition system which was designed and developed by Apple Inc. It revolutionised the authentication technology as it progressed from Touch ID(authentication using the fingerprint) to Face ID. Face ID is available for the iPhone (X, XS, XS Max, XR, 11, 11 Pro, 11 Pro Max) and also for iPad Pro(third and fourth generation). Face ID uses a number of advanced technologies to map the geometry of your face correctly. It can be used as the source of authentication for making payments, unlocking your device and keeping the information safe.

Face ID can be used to authorize purchases from the iTunes Store, App Store and the like. Apps that support Touch ID will support Face ID. It was initially released in the iPhone X in November 2017.

Face ID is a very significant advancement from the Touch ID. There is a TrueDepth camera that captures accurate face data. This is done by projecting and analysing over 30,000 invisible dots thus creating a depth map of one's face. It is also programmed to capture an infrared image of the face. Even if you are wearing cosmetic makeup or have grown some facial hair, Face ID will still be successful in recognising and authenticating you. Hence it evolves with the changes in your face. The Face ID will be temporarily disabled and the user's passcode will be required  after 48 hours of inactivity, the device has received a remote lock command, 5 unsuccessful scans, restarting the device, or if two of the device's side buttons are held briefly. It can also be used to create live effects such as camera filters and Animoji. It also prevents spoofing and other such cyber attacks with the help of anti-spoofing neural technology. The Face ID data is not stored anywhere else, it will never leave your device and hence the privacy is not compromised. Your face data is protected by a secure complex in the Bionic chips. All the processing is done on the chips. Hence your face data is not sent to a server.

Face ID also has an accessibility feature to support those who are blind or have low vision. If you don't want Face ID to need you to look at your device with your eyes open, you can always open Settings General Accessibility, and disable the Require Attention for Face ID.

Face ID uses something called as a "TrueDepth camera system". This system comprises of sensors, cameras, and a dot projector at the top of the iPhone display  to create a detailed 3D map of your face. Every time you look at your phone, the system will conduct an authentication check which enables your device to be unlocked or for your payment to be authorised. 

Each time you glance at your iPhone, the TrueDepth camera system will be able to detect your face with a flood illuminator, This is made possible even in the dark.

An infrared camera will then take an image, over 30,000 invisible infrared dots will be projected on your face with the help of a dot projector. This system uses the infrared image  and pushes them through neural networks to create a mathematical model of your face. Face ID also works with numerous third-party apps, including many banking apps. 

The issue is that some inconsistent results have been observed when testing Face ID on identical twins, close relatives etc. It is essential to set us a passcode in a case as such. But overall, it is indeed a very secure and convenient way to authenticate and use a device.