Other possibility: Ios allows you to register a second face to unlock the device through face id. Could it be that they registered their face on the device?
I realized another thing that can happen is that if you have two sufficiently similar looking people. Basically person B tries to use their face to unlock A’s phone and then A unlocks it.
If they are sufficiently similar the phone could theoretically expand its knowledge of what A looks like so that B’s face triggers a positive match.
I have no idea how close in appearance they’d need to be for Faceid to do this though.
Not rare. Approximately 80% of people have a brother or sister. On average siblings are less than three years apart, and share 50% of their genes. Children from the same parents tend to look alike.
Apple has researched this:
> 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). […] The probability of a false match is different for twins and siblings that look like you as well as among children under the age of 13, because their distinct facial features may not have fully developed.
The very last people I would want to expose my secrets to, would be family members. Whereas if a stranger hacked into my phone, beyond those secrets that have some fixed frame of reference, such as Bank Details and Social Security Number etc, a lot of other information is context-less and therefore hard to determine whether it has value. Siblings on the other hand would know the value immediately; "you sent [x] to person [y]", 'you said [z] about [a]".
My brother was able to unlock mine through Face ID even though my phone had only one face registered.
Face ID updates you face as it changes[0]. So, I guess whenever my brother used my phone it added my brother's face features since algorithm probably found some similarities in face features.
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[ 3.0 ms ] story [ 74.3 ms ] threadIf they are sufficiently similar the phone could theoretically expand its knowledge of what A looks like so that B’s face triggers a positive match.
I have no idea how close in appearance they’d need to be for Faceid to do this though.
Apple has researched this:
> 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). […] The probability of a false match is different for twins and siblings that look like you as well as among children under the age of 13, because their distinct facial features may not have fully developed.
https://9to5mac.com/2017/09/27/face-id-iphone-x-white-paper/
Family members unlocking phones documented previously:
https://www.theverge.com/2017/11/14/16650394/10-year-old-unl...
http://mashable.com/2017/10/31/putting-iphone-x-face-id-to-t...
Face ID updates you face as it changes[0]. So, I guess whenever my brother used my phone it added my brother's face features since algorithm probably found some similarities in face features.
[0] https://www.theverge.com/2017/9/27/16373710/face-id-iphone-x...