Brake-pad sensors or pad-wear indicators are devices used to indicate to the user when the brake-pad material is low and needs replacing. Brake-pad sensors come in two different types – Mechanical and Electrical.
Mechanical type sensor:
This type of sensor is a metal clip that is attached with the brake-pad. After sufficient brake-pad material has worn down, the rotor disc will come into contact with the clip. This will cause an audible screeching sound to be heard which signals new brake-pads are required. This is generally found used sensor in Japanese and American manufactured cars.
Electrical type sensor:
This type of sensor is an electrical wire attached with the brake-pad. After sufficient brake-pad material has worn down, the electrical wire will disconnect and turn on the warning light in the car dashboard. This type of sensor can be found generally in luxury-class cars or European manufactured cars.