The information was released on Google's blog.  Adding face unlock puts the Pixel 4 on par with modern iPhones for unlocking. Google also confirmed that the Pixel 4 will use the face unlock feature for payments: "face unlock works in almost any orientation -- even if you're holding it upside down -- and you can use it for secure payments and app authentication too".

Google says that biometric data will be stored locally in a secure chip and never be shared with other Google services. The Pixel 4's face unlock feature will use a variety of sensors to identify your face, including depth, infrared, and RGB. That should mean that it will work in a variety of lighting situations and work with a diverse set of faces.

As for the "Motion Sense" feature, there's not a ton that we can glean from Google's article. Earlier rumors have pointed to it being related to Project Soli, which uses radar to detect tiny hand or finger movements above the device.

Google has previously demoed rubbing your thumb and index finger together to simulate turning a dial on a smartwatch. Some code found in the next version of Android has suggested it could be used for media controls.

Google's post cites a possible use case where the Soli chip could detect your hand reaching for the phone, which would automatically turn on "the face unlock sensors." If it all works, the phone would automatically unlock itself and be ready by the time you're looking at it.