Sensor system with a sensor device comprising - a through-flow cell (2) for liquid (5-1, 5-2), - a detector device (6) for measuring a property of the liquid in the cell, for generating an associated detector signal, - a sensor control (7) for analysing the detector signal, characterized in that the sensor control is configured to detect a liquid transition (8) between two different liquids in the cell when a change (per unit time) in the detector signal is greater is than a threshold value. In the case of such a liquid transition detection, the sensor control generates an alarm signal. Liquid transition detection is carried out by means of optical, temperature and/or conductivity sensors.
