Abstract: A device for detecting harmonics in a current carrying conductor, comprises current probe for placing adjacent a current carrying conductor, the current probe generating an output signal in response to the current in the conductor; a circuit operably connected to the current probe for processing the output signal from the current probe; the circuit including a switching portion responsive to the output of the current probe for automatically turning on or off the circuit when the current probe senses current in the electrical conductor; and a display for the output of the circuit for indicating the presence of harmonics in the conductor. The display includes a plurality of various colored LEDs that are lit depending on the severity of the harmonics of interest that are detected. The circuit also includes a microcontroller for computing the Fourier coefficients of the harmonics of interest and an automatic gain control feature for auto-ranging for various current inputs from the current probe.