KD-3 is a capacitive proximity switch that uses a combination of analog and digital techniques to detect a change of capacitance on a remote sensing plate. The capacitance change is brought about when the sensing plate is approached or touched. Upon activation, a normally open relay closes, indicated by a red LED lighting. Three modes are available: Pushbutton, in which the relay stays closed for as long as presence is sensed, pulse, in which the relay closes for one second and then opens, or toggle, where the relay closes on the first touch, remaining closed until a second touch occurs. KD-3 can work with sensing plates of various sizes and shapes. The sensing plate needs to be of metal, such as copper or aluminum, although others will also work. In certain cases the artifact itself may be used as the sensor, as in the case of a metal teapot or bowl. In other cases, the sensor may be embedded in the object, provided that the object is non-metallic. The KD-3 is normally mounted close to the sensor, with a single wire connecting the two. By use of coaxial cable, this distance may be extended to several feet.Auto-calibration feature adjusts the KD-3 continuously to the environment. Such things as dirt, humidity, ice or damage to the sensor plate are automatically accounted for.