It is often difficult to synchronize OMA sensors when the distance between sensors is large. Sometimes GPS can be used for synchronization, but not always since GPS require visibility of a certain number of satellites. Other times cables or radio signals can be used, however, in some cases a direct synchronization is difficult or impossible. The focus of this paper is on synchronizing sensors by using the modal response of the considered structure. The technique assumes that only a single mode is present in the signal, and that the phase relationship between the different measurement points is known. The background for the technique is introduced and it is illustrated on response data from the Great Belt Bridge.