A device for reversing the blood flow for an extracorporeal blood treatment device, which has an extracorporeal blood circuit, includes an arterial blood line leading from a patient to a blood treatment unit and a venous blood line leading from the blood treatment unit to the patient. Furthermore, an extracorporeal blood treatment device includes a device for reversing the blood flow, and a method includes determining the reversal of the blood flow during an extracorporeal blood treatment. The device for reversing the blood flow for an extracorporeal blood treatment device includes two valve bodies which are rotated relative to one another for reversing the blood flow. The device for reversing the blood flow includes a communication device for receiving an electromagnetic high-frequency field from a read unit of the extracorporeal blood treatment device and for generating at least one identifier characterizing the position of the valve bodies which can be read by the read device.