To address this and/or other needs, the present inventor devised, among other things, a passive moisture detection probe that can be installed and left in place to continuously indicate whether the moisture-content in the wall-cavity of a building is below or above a desirable level. One exemplary moisture detection assembly includes a moisture-absorbent sensor element and an indicator. The sensor element, which can be placed in contact with the inner surface of a home's exterior sheathing, expands and contracts in response to the moisture content of the sheathing. The indicator, for example a rod, moves in responsive to the expansion and contraction of the sensor element, with its relative position corresponding to the moisture in the exterior sheathing and thus providing an on-going and observable sign of moisture intrusion.