HM DIGITAL FM-2 Water Filter Monitor with 5-Stage Volumizer and Timer Flow Sensor and Filter Indicator Disc +/- 1% Accuracy A five-stage filter monitor with five independent timers and a tri-color LED faucet indicator disc. The volumizer counts up in gallons or liters (settings can be modified). Works on time (and volume for the FM-2) for up to five stages (can be less). The LED indicator disc will illuminate a green yellow or red light when the water is turned on. The color indicates the percentage of elapsed time. Auto-Off function conserves battery power.