ABS sensors are electromagnetic devices monitoring wheel speed for the Anti-lock Braking System. Typically mounted near each wheel hub, they generate an AC voltage signal proportional to rotational velocity via a toothed tone ring (reluctor ring) or magnetic encoder. These signals are sent to the ABS control module to detect impending wheel lockup during braking events. Sensor types include inductive, Hall effect, and magnetoresistive, differing in signal strength and susceptibility to electromagnetic interference. Modern sensors often integrate with vehicle stability control and traction control systems, requiring precise calibration and consistent output.