I have one of these and the Indie Seth in Jax FL uses one of these when doing a inspection. It will tell you if your brake fluid has a certain level of moister. I just checked the Brake fluid in my Truck and it has been over two years and needed to be changed. Moister was bad! Better pedal now since changing fluid.
https://www.walmart.com/ip/Brake-Fluid-Moisture-Tester-Auto-Car-Truck-Diagnostic-Testing/169181238