A device is configured to monitor the integrity of a connection system between first and second fluid containing systems comprising first and second pulse generators. A pressure sensor is arranged in the first fluid containing system to detect first pulses originating from the first pulse generator and second pulses originating from the second pulse generator. The device operates a monitoring method, by generating (42) a time-dependent pressure signal based on measurement data obtained from the pressure sensor such that the pressure signal contains a sequence of apparent pulses. The apparent pulses represent a superposition of the second pulses on the first pulses when the connection system (C) is intact. The device processes (44) the pressure signal to calculate a parameter value based on a pulse feature of at least one of the apparent pulses in the pressure signal. The parameter value represents a disturbance caused by the superposition of the second pulses on the first pulses, and may be given as a measure of statistical dispersion, pulse-to-pulse symmetry, or first pulse similarity. The device determines (45) the integrity of the connection system based at least partly on the parameter value. The first fluid containing system may be an extracorporeal blood circuit, and the second fluid containing system may be a human or animal subject.
