device includes a housing 16 from which a microdialysis probe 17 protrudes in addition to various other devices for blood sugar measurement a fluid system according to the present invention may be arranged in or on the housing 16 from a fluid reservoir located inside the housing 16 fluid may be conveyed through a fluid line 18 to a fluid line 19 which is routed in a slit located inside the probe 17 to the tip of the probe and from there back into the housing 16 through the flow system a measurement solution may be conveyed from the housing 16 through the fluid line 19 with the aid of the probe 17 into the tissue of a patient and then conveyed back again the fluid line 19 may include a semi permeable membrane so that the measurement solution may interact with the environment surrounding the tissue in the event of a malfunction of the fluid system for example in the event of a leak in the fluid line 19 it may be possible for the measurement solution to pass from the flow system into the tissue this can pose a risk to the patient and the blood sugar measurement will not be performed correctly a wire like electrical conductor 20 may be arranged in a spiral formation around the fluid line 18 on the housing 16 in such a way that along its windings it borders the fluid line 18 in a malfunction of the fluid system in the measurement device as described above the pressure in the fluid line 19 drops sharply or is lost altogether this change in pressure may for example be recorded by a pressure sensor inside the device and the electrically activatable.