A measuring device (10) has at least one sensor (16, 18), which can be applied to the skin surface (12) of a patient for detecting a measured value with the sensor (16, 18). The device (10) has two contact surfaces (20, 22) on an underside (24), which is intended for being in contact with the skin surface (12) of the patient. A current detecting (32, 34), detects a measuring current (30) resulting from a particular effective electric resistance between the contact surfaces (20, 22). A method for operating such a measuring device (10) and a system with such a measuring device (10) are also provided.
