Five months after Google promised that it would be coming, the Pixel 4 has finally picked up an added bit of security for its face unlock system. Android 11 Developer Preview 2 has a toggle you can set for your Pixel 4 that requires your eyes to be open for face unlock to work.

The new setting, down near the bottom.

It was disabled by default on my Pixel 4, and toggling the feature on didn't require a re-setup of face data or anything like that. However, I should note that the setting didn't stick for me the first couple of times I enabled it, leading me to believe it was broken initially. Be sure to back out of the menu after you toggle it before trying to lock your device and test it. Once it's actually enabled, it seems to stay on, though.

In my testing, the new feature works both with and without glasses in multiple types of lighting, adamantly refusing to unlock my phone unless my eyes were wide. Even a stoner-like half-lidding was enough for it to say no to me, it wants them open. 

We might see this roll out to Pixel 4 phones on Android 10 later via some other mechanism like a Play Services update or a Pixel Feature Drop (the next one should land sometime around June), but it's live in Android 11 for the Pixel 4 as of Developer Preview 2.