Cars without fancy sensors have a low-tech way to tell you that your brake pads need changing: they squeal like angry piglets. They screech like baby bald eagles waiting to be fed. They scream like your mother did whenever you came home after curfew. You get the idea. It's not pleasant.
But thanks to modern sensor science, your car can tell you when the brake pads are getting thin and losing their stopping power. Better yet, your automotive robot overlords will tell on you. BMWs and Acuras both will use their on-board communications capabilities to call the dealership to tell them that you're a menace to other drivers, and the car fears for its own safety. Or they'll relay a simple code, and the dealer will call to set an appointment at your convenience. Whichever.