The present invention relates to a device and a method for monitoring a patient access, in particular a vascular access in extracorporeal blood treatment, in which a patient's blood is withdrawn from the patient via an arterial conduit and is returned to the patient via a venous conduit. The blood is conveyed by a blood pump, preferably an occlusive blood pump, such as a roller pump. To monitor the vascular access, the electrical AC voltage and/or the alternating current and/or a derived electrical measured variable that is generated by electrostatic charges during operation of the occlusive peristaltic pump is monitored. If the triboelectric AC voltage generated by the blood pump and/or the alternating current and/or the derived electrical measured variable lies within predetermined limits, this indicates that the vascular access is faulty.