Fisher Labs Gemini-3 Metal DetectorFisher Labs Gemini 3 Metal Detector Two box metal detectors are used by prospectors, geologists, treasure hunters and public utility companies to locate large, deep objects, ore veins, pipes and cables. Fisher Labs, the recognized leader in the field, was granted the first two box metal detector patent in 1938. The GEMINI 3 is respected for being the best there is because it goes deeper, traces farther and is easier to use than any other cache finder