Which tool is commonly used to measure moisture levels in walls?

A moisture meter is the correct answer because it is specifically designed to detect and measure moisture levels in materials such as walls, wood, and other surfaces. These devices are crucial in building inspections to identify areas prone to water damage, mold growth, or structural issues caused by excess moisture. They work by using sensors to measure the electrical conductivity or resistance in the material, which varies with moisture content.

While a digital thermometer measures temperature, it does not provide information about moisture levels. A laser level is used for ensuring that surfaces are level or plumb, which is unrelated to moisture measurement. A wire gauge, typically used for determining the thickness of wires, has no relevance in assessing moisture in building materials. Therefore, the moisture meter stands out as the essential tool for this specific purpose.