A device and method providing audio-based, continuous authentication of a user to provide access to a processing device. A user echoprint model is created while a user interacts with an authentication interface for another authentication method of the device, transparently to the user. The sound waves are user-specific and inaudible. The user-specific sounds are reflected by the user and used to construct an echoprint which can be compared by a previously constructed user-specific, echoprint model. If the result is positive, access to the processing device may be allowed. Access to the processing device is based on the audio authentication or the alternative authentication is based on the result of audio authentication and updates a device state indicating whether the display is on or off and whether the device is locked or unlocked.