Zero speed switches are used to detect the stoppage of a rotating shaft. They typically have one or more relays and may provide analog outputs. Zero speed switches use electromechanical, electronic or magnetic proximity technologies. Electromechanical speed switches are direct-coupled, speed-indicating devices which open or close a set of contacts mechanically, as a function of the rotational speed of the switch shaft. The construction of the switch and adjustments to internal components determine the speed at which an electromechanical switch trips. Electronic speed switches are direct-coupled, speed-indicating devices that open or close a set of contacts through a relay and electronic circuit. User-defined settings and the rotational input speed of the shaft determine the speed at which an electronic zero-speed switch trips. Magnetic proximity switches are non-contact devices which use a proximity sensor to detect a rotating piece of ferrous metal. These zero speed switches use a microcomputer to count between sensor impulses and circuitry to analyze discrepancies in pulse time. If the impulses depart from preprogrammed limits, a relay opens or closes a set of contacts.