© AppleThe iPhone X uses facial recognition to to unlock itself
The iPhone X, which is set to go on sale next month, uses a facial recognition system called Face ID to unlock phones, verify payments and gain access to apps. It has an array of sensors at the top of the phone that scan the users' face and compare it to the model stored on the phone.
Apple says the chances of an imposter being able to trick the system are one in a million, making facial recognition more secure than the one in 50,000 chance that somebody else could fool a phone's fingerprint scanner.
However, in a security paper on Wednesday it said that since under-13s' faces are still developing, there is a greater chance that the feature may not work as intended and other children - especially brothers or sisters - will be able to unlock the phone.
"The [one in a million] 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," Apple said. It recommended using a PIN code on the phone to lock it instead.
The iPhone X, which was first unveiled two weeks ago, will cost a minimum of £999 when it goes on sale next month, so it is unlikely to be a popular choice for parents buying their child's first mobile phone.
Its facial recognition cameras and sensors project thousands of invisible light beams onto the user's face, creating a three-dimensional model so that it cannot be fooled by photographs.
Apple says it has enlisted Hollywood studios to make sure realistic face masks do not unlock the phone and that users' privacy is protected because the data never leaves the phone itself.
To work, the cameras have to be able to see the user's eyes, nose and mouth, so burkas, niqab and balaclava wearers will not be able to use the feature. However, it can see through beards, hats and glasses.
Comment: Facial recognition in the wrong hands: Don't trust the police around your new iPhone X