The feature is supposed to be the alternative for biometric security to the fingerprint. Something which stayed behind on the Pixel 3 and Pixel 3a.
Google has reportedly said that its Face Unlock feature meets security requirements as a strong biometric. However, BBC's report notes that a security expert deems it a problem.
Stating that "it's a significant problem that could allow unauthorized access."
Google confirms Face Unlock works with eyes closed on retail units
Pre-release units of the Pixel 4 apparently had a toggle which dictated eyes needing to be open. Retail units however do not have this option.
According to BBC, who got confirmation from Google, retail units will allow Face Unlock to work even if your eyes aren't open. There's potential for this change in the future.
Google says that it will continue to improve Face Unlock over time. And, since pre-release units had a toggle that required your eyes to be open, Google could always add it later. Whether or not it will is another thing entirely.
A potentially big problem
Cyber-security expert Graham Cluley says this could be a big problem. Noting that someone could unlock the device without your permission while you're asleep.
Since it's confirmed that your eyes don't need to be open, this could certainly become an issue for some users. It would be an easy thing for kids or an untrusting partner to hold the phone up to the owner's face and have it unlock.
Google does note though that if people want enhanced security there is a sort of fix. Though, it requires disabling facial recognition. To do this, users would need to enable "lockdown mode," which would turn facial rec off. Which in turn would render Face Unlock useless.
This would also mean that users would have to revert to using PINs, passwords, or patterns for unlocking the phone. It's slightly less futuristic than Face Unlock or fingerprints, but in this particular case it would be more secure.
And in the end that should be the main takeaway. Especially if you're worried about the unlock method being used without your personal authorization.
The Pixel 4 is Google's latest smartphone, which it revealed to the public on October 15. Aside from Face Unlock, it has other new features, such as Motion Sense, which uses the integrated Soli chip powered by radar technology for hands-free interaction.