Test moisture levels between 0 (dry) to 10 (moist). Monitor pH levels between ph0 (acidic) and pH10 (basic). Read light levels between 0 (low) to 2000 (very strong). Do not leave in soil; clean prongs after each use. Great for indoor or outdoor use; no batteries needed. Simplifying the science of soil, the Hydrofarm ActiveAir 3-Way pH with Light and Moisture Meter helps gardeners monitor the health and balance of their favorite plants. Great for use indoors or out, this piece doesn't require batteries for reliable use, season after season. Simply dip the meter into the soil and read moisture levels so you know when to water, pH levels so you know when to fertilize, and light levels so you know if you need to re-place. Perfect plants don't get easier than this! About Hydrofarm, Inc. Celebrated as the nation's oldest and largest manufacturer of hydroponic equipment and grow lights, Hydrofarm has made professional-grade equipment available to all since 1977. All grow lights and electric components are UL listed, unlike many competitors' products, meaning you get years of reliable and safe use out your high-intensity lights. All products are covered by a one year warranty, at the least. In some cases Hydrofarm ensures the performance of their products for five years.