Abstract: The present invention provides an improved gas/fluid detector for use in contained fluid systems, and is particularly apt for medical applications wherein fluids are transfused to a patient. The invention includes directing energy pulses into a fluid containment region of interest, detecting energy at the region of interest during each of a plurality of intervals associated with the energy pulse, generating a multi-component detection output utilizing the detected energy for each of the time intervals and separately employing each of the components of the multi-component detection output to determine whether a predetermined condition exists within the contained region of interest. Such predetermined condition may be one of the absence/presence of fluid/gas. Preferably, a multi-component detection signature is provided in the form of a digital serial output and compared with a reference signature that is provided in a corresponding digital serial output.