Function: The moisture meter of the brake fluid tester of the upgrade version can extensively test the moisture content of DOT3 DOT4 DOT5 brake fluid. It has faster and more accurate reading skills than similar products while being more extensive. LED lights: thanks to the 5 LEDs, the water content in the brake fluid will accurately display from 0% to more than 3% in 5 levels. Brake fluid is hygroscopic and over time the water content gradually increases. Red light means the brake fluid needs to be replaced immediately, green light means it is in good condition, and yellow light means it is in good condition but needs to be replaced soon. Automatic shut-off: the brake fluid tester is easy and convenient. It only takes a few seconds to check the quality of the brake fluid of the car. It is a must have because it is small and easy to carry. It also switches off automatically if not used within 12 seconds to save battery power. (Requires 1 x AAA / 1.5 V battery, not included) Quality: the brake fluid tester pen is the perfect tool to update after many researches on similar products on the market. Read more accurately during testing. At the same time, its shell material is made of high-quality nylon compared to ABS material. The product is more corrosion resistant and has a longer service life. An Excellent Helper for Your TravelThe brake fluid detection pen is based on the change of electrical conductivity to measure the moisture change of the brake fluid. It clearly shows the moisture level through the light diodes. A high moisture content lowers the boiling point, affects the braking performance and also corrodes the main brake cylinder and the wheel cylinder, which leads to rust and stuck.