The huey and huey Pro are colorimeters made by X-rite and sold by Pantone to calibrate color monitors. They are no longer in production.
It is a small device about the diameter of a pencil and only several inches long. It works in conjunction with special purpose software which displays a series of white, gray, and colored patches on the screen. After measuring these patches, it computes new LUTS, and if the OS supports it, ICC profiles, for the monitor.
It also contains and ambient light sensor and it adjusts the calibration to changing room lighting conditions.