This easy one-click TDS test pen offers effortless one-button operation to quickly detect total dissolved solids in all types of water, ideal for daily household and light commercial water purity inspection. Fitted with a high-sensitivity precision electrode sensor, it provides stable, accurate readings covering a wide measuring range of 0–9990ppm, built with automatic temperature compensation to fix data deviation from changing water temperatures. The clear digital LCD screen supports a handy data hold function to lock test values for convenient recording, plus an auto shutoff feature to avoid unnecessary battery drain after idle use. Crafted with lightweight splash-resistant ABS plastic and a detachable protective probe cap, its slim pen-shaped body fits easily in pockets for portable on-site testing. Factory pre-calibrated out of the box, no complicated setup is required for first-time use. Widely applied to test drinking tap water, bottled purified water, hydroponic nutrient solutions, fish aquariums and small laboratory water samples, this budget-friendly one-click TDS pen is a practical water monitoring tool for families, growers and water treatment enthusiasts.