Apple published a support document, detailing some interesting features and functions of Face ID.

Face ID automatically adapts to changes in your appearance, such as wearing cosmetic makeup or growing facial hair. If there is a more significant change in your appearance, like shaving a full beard, Face ID confirms your identity by using your passcode before it updates your face data. Face ID is designed to work with hats, scarves, glasses, contact lenses, and many sunglasses. Furthermore, it’s designed to work indoors, outdoors, and even in total darkness.

Face ID will be a problem for people who use anti-smog masks, which is pretty much most of Asia. This could be potentially solved by enrolling two faces — with and without a mask on — but as far I as understand, it is currently only possible to enroll one face per device. This could change in the future.

Face ID data – including mathematical representations of your face – is encrypted and protected with a key available only to the Secure Enclave.

The probability that a random person in the population could look at your iPhone X and unlock it using Face ID is approximately 1 in 1,000,000 (versus 1 in 50,000 for Touch ID). As an additional protection, Face ID allows only five unsuccessful match attempts before a passcode is required. The statistical probability is different for twins and siblings that look like you and among children under the age of 13, because their distinct facial features may not have fully developed. If you’re concerned about this, we recommend using a passcode to authenticate.

I would be extremely interested in seeing Face ID tested on twins. Luckily, I’m sure someone will attempt to.

Face ID matches against depth information, which isn’t found in print or 2D digital photographs. It’s designed to protect against spoofing by masks or other techniques through the use of sophisticated anti-spoofing neural networks. Face ID is even attention-aware. It recognizes if your eyes are open and looking towards the device. This makes it more difficult for someone to unlock your iPhone without your knowledge (such as when you are sleeping).

I won’t even try spoofing it with a photo, like I successfully spoofed my review Galaxy S8 — I’m pretty sure they got this covered.

Face ID data – including mathematical representations of your face – is encrypted and protected by the Secure Enclave. This data will be refined and updated as you use Face ID to improve your experience, including when you successfully authenticate. Face ID will also update this data when it detects a close match but a passcode is subsequently entered to unlock the device.

Face ID data doesn’t leave your device and is never backed up to iCloud or anywhere else.

Piece of mind.

Even if you don’t enroll in Face ID, the TrueDepth camera intelligently activates to support attention aware features, like dimming the display if you aren’t looking at your iPhone or lowering the volume of alerts if you’re looking at your device. For example, when using Safari, your device will check to determine if you’re looking at your device and turns the screen off if you aren’t. If you don’t want to use these features, you can open Settings > General > Accessibility, and disable Attention Aware Features.

Others have done this before, but it appears that Apple’s approach to implementing this feature is superior — at least it won’t pause playing video when a person looks away.

Within supported apps, you can enable Face ID for authentication. Apps are only notified as to whether the authentication is successful. Apps can’t access Face ID data associated with the enrolled face.

Craig Federighi already mentioned that apps not updated to support Face ID, but which support Touch ID, will work “out-of-the-box”.

The system will not cause any harm to eyes or skin, due to its low output. It’s important to know that the infrared emitters could be damaged during repair or disassembly, so your iPhone should always be serviced by Apple or an authorized service provider. The TrueDepth camera system incorporates tamper-detection features. If tampering is detected, the system may be disabled for safety reasons.

I’m sure some people will complain about issues with their TrueDepth camera being deactivated after an unauthorised screen exchange or some other service work, but I prefer to have piece of mind in this regard.

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While I’m still not sold on Face ID — it could turn out to be a hassle — I’m very curious about the attention-aware features. Those could be a really nice perk.