A method for authenticating a current user of a first communication system with respect to a second communication system by means of a behavior-based authentication carried out using the first communication system and the second communication system, the first communication system comprising a mobile, portable communication system carried by the user and a first interface, which is configured to communicate with the second communication system, the first communication system comprising a first sensor, which is configured to detect data, the data encompassing behavior-based data of an individual intrinsic behavior of the user, the first sensor, serving as a movement sensor for detecting movements of the first communication system, being configured to detect movement data, serving as data, of a gross motor-related movement of the current user of the first communication system, the second communication system comprising a second interface and a third interface, the second interface being configured to communicate with the first communication system via the first interface, the third interface being configured to communicate with at least one activatable device, the second communication system comprising a second sensor, which is configured to detect data of the user, the method comprising: - receiving a first interim result of the behavior-based authentication from the first communication system by the second communication system via the first interface and the second interface, the first interim result having been generated by the first communication system, using the behavior-based data detected by the first communication system; - generating a classification result by the second communication system from the first interim result and a second interim result, which was generated by the second communication system, using the data detected by the second communication system; - evaluating the classification result according to a predefined examination criterion by the second communication system; and - activating the device by means of a control signal by the second communication system via the third interface as a function of whether the classification result meets the examination criterion, the user being authenticated if the classification result meets the examination criterion. - receiving a first interim result of the behavior-based authentication from the first communication system by the second communication system via the first interface and the second interface, the first interim result having been generated by the first communication system, using the behavior-based data detected by the first communication system; - generating a classification result by the second communication system from the first interim result and a second interim result, which was generated by the second communication system, using the data detected by the second communication system; - evaluating the classification result according to a predefined examination criterion by the second communication system; and - activating the device by means of a control signal by the second communication system via the third interface as a function of whether the classification result meets the examination criterion,