An optical sensor system comprises one or more optical sensor devices, a master device and an electrical bus connecting the sensor devices to the master device. The bus comprises a signal daisy chain for the transmission of synchronization events. The sensor devices are adapted to detect a synchronization event at a signal input terminal, to time an optical activity based on this synchronization event and to provide at a signal output terminal a synchronization event delayed by an offset time with respect to the detected synchronization event. A property of the synchronization events provided by the sensor devices is indicative of an output value of the respective sensor device, corresponding to a state of an optical section to which the sensor is sensitive. Diodes are connected between the signal output terminals of the sensor devices and a signal line of the bus, which is connected to a signal input terminal of the master device, so that the latter receives the synchronization events from the sensor devices. The master device comprises means for extracting the output values of the sensor devices from these synchronization events. A sensor device for such a system comprises an enclosure of cuboid outer shape adapted to be mounted to a mounting rail so that the longitudinal direction of the rail is perpendicular to lateral sides of the enclosure. An electrical connector with the signal input and output terminals and with power supply terminals is arranged at a side connecting the lateral sides of the enclosure. Bus segments are provided for connecting the sensor devices to the system bus.