KAIWEETS Brake Fluid Tester Pen with Corrosion Resistance Probe, High-Precision Brake Fluid Moisture Tester with Data Hold Function, Buzzer Alarm, 3 Colors Backlight, Calibrated for DOT3, DOT4, DOT5.1

I've used this brake fluid electronic moisture content tester two dozen times since purchasing it and can report good results with DOT 4 fluids. I find this instrument to be well made, reliable and easy to use. I believe the tester measures the electrical conductivity of the brake fluid to determine its moisture content. The LED indicators provide a clear, easy to understand representation of the condition of the fluid. Brake fluid is hygroscopic, meaning it absorbs moisture over time. Excess moisture (3+% ) can lower the boiling point of brake fluid, leading to potential brake failure. In my case, the color of the brake fluid had darkened from bright yellow to olive green over time, which got my attention. In addition to causing reduced braking force, excess moisture in brake fluid can cause internal corrosion of the brake pipes and system components. In my opinion, annual testing of brake fluid is important for maintaining braking system quality/reliability and this tool gets the job done easily and efficiently. Satisfied customer here. Hope this helps...

Super easy to use giving accurate results that can be read directly from % numbers or green, yellow or red lights! Also gives warning sounds! Bright lights are easy to see in the shop. Durable heavy plastic housing with sealed test probs. Runs on common A batteries. Great value for the money! Don’t guess around with the safety of your brake system! Test your brake fluid and replace when needed! FYI: for testing purposes in the photos I had a drop of water on my finger tip!!!

Works great and it’s accurate. Worth the money.

I'd give this KAIWEETS brake fluid tester pen a solid 4 stars. It works as advertised—insert the corrosion-resistant probe into the brake fluid reservoir, and within seconds you get a clear reading on moisture content with the 3-color backlight making it easy to interpret the results at a glance. The buzzer alarm adds a useful audio confirmation, and the data hold function is a practical touch that lets you read the result without rushing. Being pre-calibrated for DOT3, DOT4, and DOT5.1 covers the most common brake fluid types, which makes it a versatile tool for checking multiple vehicles. For basic brake fluid maintenance and safety checks on cars, trucks, and the RV, it gives a quick, reliable snapshot of fluid condition without any guesswork. The only reason I'm holding back a star is that it's a single-purpose tool, but for what it does it performs reliably and is well worth having in the garage for routine vehicle maintenance.

Works well. Very durable. Easy to read. Used it on all my vehicles. Even checked the brake fluid bottle that I purchased from the store.

Works great. Easy to use.

Pretty affordable, and a good sized tool that does it job. Really can’t ask for anything else. It’s exactly what it claims to be.

Never seen these before but wanted one. Tested an old open bottle of ten year old fluid it tested bad. New bottle tested good and four year old fluid in truck tested in the middle ( good but expected to change soon ). So happy with results and did disposed of old open fluid . It will be handy to check others as needed