Now the smartphone is able to "recognise" the owner's face "better over time" thanks to the latest improvement in the Pixel Features Drop.
Google states: "When it's on, face unlock images are occasionally used to create improved face models.
"This helps recognise you better over time."
The Face Unlock works even if a person has their eyes closed.
The tech giant confirmed ahead of the phone's release that the security system allows access to a person's device even in the event their eyes are shut.
In a statement, the company said: "Pixel 4 Face Unlock meets the security requirements as a strong biometric."
As a comparison, Apple's Face ID system makes sure the user is "alert" and facing the phone before it can be unlocked.
Before the model was launched, the Pixel product manager Sherry Lin insisted: "There are actually only two face [authorization] solutions that meet the bar for being super-secure. So, you know, for payments, that level - it's ours and Apple's."