Welcome to the age of Soli. Google has shown us how the Soli Sensor will do a couple of neat tricks in the Pixel 4, and while waving your hand like a Jedi to change what song is playing is pretty self-explanatory (and honestly, not that exciting), using it in tandem with dedicated hardware to unlock your phone with your face is something we haven't seen before.
This isn't the face unlocking you're used to seeing.
Facial unlocking, however, is something we've seen before. First debuting on Android 4.0 Ice Cream Sandwich with the Galaxy Nexus, using your phone's selfie camera — or, in newer iterations, infrared cameras— to unlock your phone is an incredible experience. It's also fairly fast, easy to use, and until Apple developed Face ID on the iPhone X, extremely insecure. Face unlock that only uses a camera to capture data on a two-dimensional plane is easy to fool with a photo. That made it more of a convenience feature, one even Google said shouldn't be used if you value security.