Device for monitoring an extracorporeal blood circuit for an extracorporeal blood treatment device, where the extracorporeal treatment device has an extracorporeal blood circuit (I) with an arterial branch (6) leading to a blood treatment unit (1 ) and has an arterial connection with the patient (5) and a venous branch (7) that extends from the blood treatment unit where venous closure unit (17) is provided upstream of a venous connection of the patient (8 ) and has a blood pump (9) to provide blood to the extracorporeal blood circuit； The monitoring device has a control and computing unit (15) configured so that a first and second method can be performed to monitor the arterial and / or venous access, in each of them at least the presence of a characteristic criterion of a condition of vascular access that is outside an adequate order, the at least one criterion for the first method and the at least one criterion for the second criterion are different from each other and so that it can be established that a vascular access it is not suitable for monitoring with the first and second method, characterized in that the control and computing unit (15) is configured in such a way that a control signal is generated to stop the blood pump (9) once the presence of at least one criterion for the first method has been established, while the closing unit (16, 17) remains open and that the presence of at least one criterion of the second method is verified a Once the control signal has been generated to stop the blood pump (9), a control signal is generated to close the venous closure unit (17) if at least one second method criterion is present and a signal is generated. of control to start the blood pump (9) if at least one criterion for the second method is not present.Dispositivo para monitorear un circuito sanguíneo extracorpóreo para un dispositivo de tratamiento de la sangre extracorpóreo, donde el dispositivo de tratamiento extracorpóreo tiene un circuito sanguíneo extra
