A reviewer managed to fool the ‘attention check’ performed by Face ID on the iPhone X, which is intended to ensure that you are looking at the phone. It did, however, require a very unusual combination of circumstances …

A colleague of Gizmodo’s Alex Cranz was able to successfully unlock the phone using her face while she had her eyes closed, pretending to be asleep. This should only be possible if you choose to switch off attention-detection in the settings.

The attention check is designed to ensure that you really do want to unlock the phone by making sure that your eyes are open and you are looking at the phone.

She said that there were likely two factors at work in the feigned sleep test.

Cranz also experienced a number of failures where Face ID failed to recognize her, though one cause here was wearing glasses with a UV protective layer. Apple advised at launch that Face ID will work with most glasses but not all.

[The other] component was the makeup I applied during the Facebook Live. It’s a very heavy foundation that flattened my face on camera, it also lists titanium dioxide amongst its ingredients. Titanium dioxide is a noted ingredient in many types of sunscreen and actually reflects infrared light. Which means the makeup functions as a double whammy, preventing infrared lasers from accurately measuring the depth of markers on my face, and the camera can’t use its algorithms to make an approximate depth map of my face because the makeup severely flattens things out.

Reviewers have also been attempting to fool the phone with twins, with varying results. This is another specific situation where Apple advised that Face ID may be unable to cope.

Any biometric tech will have a failure rate of some kind, with false positives as well as false negatives, and the combination of circumstances here is really unusual, but Apple says its is investigating.

You can check out the feigned sleep test starting around 16 minutes in.