A method and a device for continuous, noninvasive monitoring of an extracorporeal blood treatment, a patient’s blood pressure or a quantity that correlates with the blood pressure is measured and compared with a predetermined limit value. The signal generator is designed for the emission of at least two signal beams covering in given relationship to each other an area and the signal receiver is designed for the time-resolved reception of the signal beams in such a manner that the generator-receiver distance can be determined from the time signature of the signal beam reception. In the event of a failure of a process, or of an entire monitored node, the monitoring nodes may collaborate to initiate a restart of the processes on the same or a substitute monitored node. All components have circular cross sectional geometry.