You could also lift a person's finger and put it on a fingerprint reader, but at least you have to touch the victim to do that. Early versions of the Pixel 4 face unlock settings had a checkbox to "Require eyes to be open," but that is not present on review units or the shipping version. The other side has this colorful power button. Listing image by Google. In addition, most Emacs faces are defined so that their attributes are different on light and dark frame backgrounds, for reasons of legibility.
By default, Emacs automatically chooses which set of face attributes to display on each frame, based on the frame's current background color. Google says it will "continue to improve Face Unlock over time. The other side has this colorful power button. Even Google's old face unlock system for Android 4.