This paper presents a new approach to combine several biometrics in a multimodal device. The proposed approach does not use typical fusion strategies but is based on the multi-dimensional cost probability densities of the originals and forgers, which can be measured or calculated from the intrinsic cost or score distribution of the single biometrics, and uses different decision strategies within this distribution. The performance of the proposed combination method is shown to be superior to that of the single biometric subsystems. The main advantage of this method is the selectable degree of security or comfort. This means that the false acceptance rate (FAR) or the false rejection rate (FRR) of the overall system can be set according to the desired requirements of the respective authentication scenario. Furthermore the approach enables the combination and integration of all biometric systems which provide the cost distribution of originals and forgers even if they come from different suppliers.