A simple tool for testing the percentage of water in brake fluid. 5 LEDs Indicate percentage of water present in fluid. Suitable for DOT 3, 4, 5 (not suitable for silicone based DOT 5.1). Automatic Power Off. Powered by 1 x AAA 1.5V Batteries (included). RoHS, CE. Indicators: Green - Battery in product is ok and no water in brake fluid. Green & Yellow - Less than 1% water present in brake fluid. Green, Yellow & Yellow - Approximately 2% water present in brake fluid. Green, Yellow, Yellow & Red - Approximately 3% water present in brake fluid. A change of brake fluid is recommended. Green, Yellow, Yellow, Red & Red - At least 4% water present in brake fluid. Urgent change of brake fluid is necessary.