This feature is called “Unlock with Apple Watch” and it allows you to unlock your iPhone using your paired Apple Watch if Face ID fails or if you’re wearing a mask.

To use this feature, you need to have an Apple Watch Series 3 or later with watchOS 7.4 or later and an iPhone X or later with iOS 14.5 or later. Additionally, you need to have enabled the “Wrist Detection” feature on your Apple Watch.