Abstract: An apparatus for effecting acoustic surveillance of a space beyond a barrier includes: (a) a plurality of acoustic sensor devices; (b) a combining unit coupled with the plurality of acoustic sensor devices; and (c) a display unit coupled with the combining unit. The combining unit receives a respective sensor signal from each respective acoustic sensor device of the plurality of acoustic sensor devices. Each respective sensor signal indicates a sensed condition in the space. The combining unit and the display unit cooperate to display at least one displayed signal representing at least one of the respective sensor signals.