A method for authenticating a user of a building locking system by means of a wall-mountable authentication device which is connected to a door actuator (22, 24) and which comprises: a control unit; an image acquisition device connected to the control unit; a sound recording/output device connected to the control unit; a device for wireless transmission/reception of data connected to the control unit; a touch-sensitive screen connected to the control unit; and an interface module connected to the control unit for connecting the authentication device to at least one door actuator (22, 24), wherein the authentication device detects a first security feature of the user in a first authentication step and compares the detected first security feature with at least one first predefined security feature and, if the detected first security feature matches the first predefined security feature, the authentication device detects a second security feature of the user in a second authentication step and compares the detected second security feature with at least one second predefined security feature and, if the detected second security feature matches the second predefined security feature, the control unit initiates an unlocking and/or opening of a door associated with the door actuator (22, 24), characterized in that, in the event that the user leaves a building equipped with the building locking system, the method for authenticating the user is started by an opening, detected by a sensor system, of a door associated with the door actuator (22, 24) and, if the security feature detected in the first authentication step matches a correspondingly predefined security feature within a predetermined time period after the detected opening of the door, the control unit initiates a locking of the door associated with the door actuator (22, 24). a control unit; an image acquisition device connected to the control unit; a sound recording/output device connected to the control unit; a device for wireless transmission/reception of data connected to the control unit; a touch-sensitive screen connected to the control unit; and an interface module connected to the control unit for connecting the authentication device to at least one door actuator (22, 24), wherein the authentication device detects a first security feature of the user in a first authentication step and compares the detected first security feature with at least one first predefined security feature and, if the detected first security feature matches the first predefined security feature, the authentication device detects a second security feature of the user in a second authentication step and compares the detected second security feature with at least one second predefined security feature and, if the detected second security feature matches the second predefined security feature, the control unit initiates an unlocking and/or opening of a door associated with the door actuator (22, 24), characterized in that, in the event that the user leaves a building equipped with the building locking system, the method for authenticating the user is started by an opening, detected by a sensor system, of a door associated with the door actuator (22, 24) and, if the security feature detected in the first authentication step matches a correspondingly predefined security feature within a predetermined time period after the detected opening of the door, the control unit initiates a locking of the door associated with the door actuator (22, 24).