The invention relates to a method for time synchronization of a plurality of different wireless networks A, B, each wireless network (A, B) comprising at least one data sensor (A.1, A.2, A.3, A.4, B.1, B.2, B.3, B.4) for measuring data and a gateway (A.0, B.0) to which the measured data is sent, wherein a common time master (TM) is used which broadcasts time synchronization messages to all networks (A, B) involved. This way, a possibility of time synchronization of a plurality of different wireless networks (A, B) in an easy, efficient and reliable manner is achieved.