A surveillance device monitors the integrity of a fluid connection between first and second fluid containing systems based on at least one time-dependent measurement signal from a pressure sensor in the first fluid containing system. The first fluid containing system comprises a first pulse generator, and the second fluid containing system comprises a second pulse generator. The pressure sensor is arranged to detect first pulses originating from the first pulse generator and second pulses originating from the second pulse generator. The integrity of the fluid connection is determined based on the presence of second pulses in the measurement signal. The second pulses may be detected by analysing the measurement signal in the time domain and/or by using timing information indicative of the timing of the second pulses in said at least one measurement signal. The analysis may be based on a parameter value that represents a distribution of signal values within a time window of the measurement signal. The parameter value may be calculated as a statistical dispersion measure of the signal values, or may result from a matching of the signal values within the time window to a predicted temporal signal profile of a second pulse. The fluid connection may be established between a human blood system and an extracorporeal blood flow circuit.