The invention relates to a device for detecting moisture which is designed as a cover 30 to be placed on the skin of a patient, and to a device B for monitoring access to a vessel. The cover 30 comprises a flexible base material 31 to which an electrically conductive structure 32 composed of conductive tracks 33, 34 is applied to serve as a moisture sensor. The device 40 is characterised in that the electrically conductive structure 32 comprises two conductive tracks 33, 34, wherein one end of the first conductive track and one end of the second conductive track comprise a first pair of connection contacts 35A, 35G and the other end of the first conductive track and the other end of the second conductive track comprise a second pair 35C, 35E of connection contacts. The first pair of connection contacts is used to connect a device B for monitoring access to a vessel, whereas the second pair of connection contacts is used to connect a terminating resistor R. The device can be produced cost-effectively in large quantities. Using the separate terminating resistor there is no danger for the terminating resistor to be destroyed as a result of movements by the patient or for the resistance thereof to change.
