Abstract: This invention is directed to a system for detecting the presence of moisture in a given location such as the attic of a building or house before the moisture has had an opportunity to penetrate plaster walls or cause other damage. The disclosed invention includes a detector for detecting the presence of minute quantities of moisture contemporaneous with their initial appearance, which responds to the presence of moisture by exhibiting a decrease in its internal impedance. An audible signal-generating circuit is coupled to the detector and responds to the resultant decrease in the impedance of the detector by commencing to oscillate at a pre-determined audio frequency.