The signal from at least one sensor (2) for measuring a physiological parameter is fed to a data processing module (4) via a signal cable (3). A display device (9) is connected to the data processing module. An expansion module (10) for transmission of telemetry data is connected to the data processing module via an interface (13). The expansion module is connected by a wireless telemetry path (21,22), such as a Bluetooth(RTM) interface, to the sensor or an additional sensor (20).