Simple four light system helps alert users to possible moisture problems. Find out if potentially damaging excess moisture is present. Detects moisture at percentages of 14% - 20%. Detects levels of moisture present in wood, sheetrock, carpets and more. Helps to select drier lumber. use to check surfaces before painting, wallpapering, or laying floors or tile, and also decks before staining or sealing. Requires one 9V battery (not included).