The sensor device serves for detecting the absence or presence of a liquid (1) at the outlet (10a) of a feed line (10) through which there can be fed a feed substance which, when exiting from the outlet, has a pressure (p) in the feed line which has a course over time with a first characteristic in the absence of the liquid and has a course over time with a second characteristic in the presence of the liquid. The sensor device includes a sensing instrument (20-23) for sensing the pressure fluctuations in the feed line (10) and evaluator (30) which is designed to assign the sensed pressure fluctuations to the first or second characteristic and to generate a corresponding signal which indicates whether the liquid (1) is absent or present at the feed line outlet (10a).