High Quality Material: Our brake fluid liquid test pen is made of nylon material, compared with ABS material, it is anti corrision. As we all know the brake oil is pretty corrosive, when you use the shell of ABS material, the plastic part of it will be corroded and dissolved by the brake oil, and the shell will be crushed after a long time using. There's no need to worry about this problem with our product. Safe and Practical: This auto brake diagnostic testing tool can check the health status of DOT3, DOT4, DOT5.1 car brake fluid. When it is time to change the brake fluid, the LED light will go from green to yellow or red, reminds you to change the brake fluid, helps you to avoid traffic accidents, provide you with a comfortable and safe driving. Easy to Read and Use: This check engine is small in size and easy to carry. Press the button and insert it, you can see the result of water content in your brake fluid. There are 5 LEDs indicating the water content in the brake fluid : 0% means there is water content in brake fluid. 1% means H2O1%, brake fluid is above standard. 2% means H2O2%, still can use it. 3% means H2O3%, brake fluid should be changed. 4% means H2O4%, brake fluid must be changed. Multiple Usage: This brake fluid detector is widely used in most cars, and it is suitable for detecting the moisture content in DOT3, DOT4, DOT5.1 brake fluid. This product has no cable connector, it's convenient and easy to use. It can be used in personal cars or repair shops. There is a small suggestion, after every testing, please clean the test probe with dry cloth or paper. Note: AAA battery required, one button operation. The battery is not included in the package. It is handy and anti corrision but please be curious not drop it on a hard surface and be careful with the battery door or the ears will snap off. In a word, with this product you can do your own annual maintenance and document it instead of change your brake fluid in case of emergency. Any questions please feel free to contact us.