A monitoring system (9) performs a method for detecting a disruption of a fluid connection between a first fluid containing system and a second fluid containing system. The monitoring system generates a monitoring signal (M1) which is representative of a fluid pressure in respect of the first fluid containing system and which is responsive to the disruption of the fluid connection, and a tracking signal (T1) which corresponds to and is more smoothed over time than the monitoring signal (M1). The monitoring system (9) further sets a detection range (M1L, M1H) in a given relation to the tracking signal (T1) so that the detection range (M1L, M1H) follows changes in the tracking signal (T1), and detects a condition indicative of the disruption by comparing a current pressure value of the monitoring signal (M1) to the detection range (M1L, M1H). The monitoring system (9) may be connected to or part of an apparatus for blood treatment and operable to detect a disconnection of an extracorporeal blood circuit from a vascular system of a patient, e.g. downstream of a blood pump in the extracorporeal blood circuit.
