[ADent]

For iPhones your eyes have to be open.

I’ve got to think some cops are good at holding up the phone and saying look at this text message and people opening eyes to see it though.

[eddyg]

Not just open, but (by default) “paying attention” and not actively trying to “look away” from the phone:

The TrueDepth camera will provide an additional level of security by verifying that you are looking at iPhone before unlocking. Some sunglasses may block attention detection.