Provided herein may be a smart watch. The smart watch may include a display device configured to display an image; a bezel disposed on the perimeter of the display device and configured to rotate; a main body configured to support the display device; and a band coupled to the main body. The main body includes a bezel sensing unit configured to sense movement of the bezel, and a control unit configured to authenticate a user based on information received from the bezel sensing unit and configured to unlock the smart watch in response to the control unit authenticating the user.