Audio monitoring system
The audio monitoring system was a system aboard Relay Station 47 used to track audio transmissions.
In 2369, Beverly Crusher asked what noises she was hearing on the relay station. Geordi La Forge suggested that an audio monitoring system had been left on and the noise was likely "a few thousand subspace messages". He went to turn it off, but was interrupted by the sounds made by "Maura" the dog. (TNG: "Aquiel")