A switch designed to perform the function of opening and/or closing one or more electrical circuits. the switching function is accomplished by means of separable contacts, semiconductor devices, or a combination of separable contacts and semiconductor devices. the item functions in response to electrical changes in its internal circuit caused by capacitance, inductance, or magnetic flux changes. it is activated by permanent magnets, metallic materials, or nonmetallic materials which come within its sensing range. for sensing switches which respond to changes other than capacitance, inductance, or magnetic flux, see switch, airflow; switch, centrifugal; switch, inertia; switch, pressure; switch, pressure-thermostatic; switch, thermostatic; and switch, tilt.