The device (18) has a measuring device (20) for measuring low pressure (Part) in extracorporeal blood circuit. An evaluation unit (21) is closed in incorrect condition when a detection device (19) detects the occurrence of air bubbles in the blood circuit and the measured low pressure lies above a given threshold value and/or the evaluation device is closed in another incorrect condition when the detection device detects air bubbles in the blood circuit and the measured low pressure lies below the given threshold value, where the former condition differs from the latter condition. Independent claims are also included for the following: (1) an extracorporeal blood treatment apparatus (2) a method for monitoring an extracorporeal blood circuit.
