Google has confirmed the Face Unlock system on its new Pixel 4 smartphone can allow access to the device even when the user has their eyes closed.
Early testers of the phone, as well as security experts, have raised concerns it could lead to unauthorised access to the device.
It has been suggested someone else could gain access to the phone by holding it in front of the face of its sleeping owner, but Google said it meets security requirements.
The technology giant unveiled the new phone earlier this week.
In a statement, Google said: “Pixel 4 Face Unlock meets the security requirements as a strong biometric and can be used for payments and app authentication, including banking apps.
“It is resilient against unlock attempts via other means, like with masks.
“If you want to temporarily disable Face Unlock, you can use lockdown mode to temporarily require a PIN/pattern/password.
“We will continue to improve Face Unlock over time.”
The help page of Google’s website related to the Pixel 4 and its Face Unlock feature also warns users: “Your phone can also be unlocked by someone else if it’s held up to your face, even if your eyes are closed.
“Keep your phone in a safe place, like your front pocket or handbag.”
It also says the phone can be unlocked “by someone who looks a lot like you, like an identical sibling”.
Apple’s Face ID unlocking system requires the user’s eyes to be open and for them to look directly into the camera in order to access the device.
The Pixel 4 is due to go on sale in the UK on October 24.