A device and method for authenticating a user of a wearable biometric device. The method involves performing an initial biometric authentication of the user, the authentication being based on biometric features extracted from one or more image frames corresponding to a first portion of the user's hand and/or wrist, captured with a camera of a wearable device. A second part of the authentication method involves either re-confirming the initial biometric authentication of the user or verifying the liveness of the user or both re-confirming the authentication and verifying the liveness. The second step of the method is based on at least a measure of a second portion of the user's hand or wrist taken when the wearable device is worn against the user's hand or wrist. A notable part of the method is that the initial biometric authentication is performed by temporarily moving the camera away from the first portion of the user's hand and/or wrist.