Hall sensor is a transducer it varies the output voltage in response to changes in magnetic field. magnet is on a shaft or hall plate . With a hall senor the control can do switching, positioning, speed detection.
it directly returns a voltage. With a known magnetic field, its distance from the Hall plate can be determined. the relative position of the magnet can be deduced.
Electricity carried through a conductor will produce a magnetic field that varies with current.
problem with them are shorts , open and misplacements...