Klein Tools, GFCI Receptacle Tester. Detects the most common wiring problems in standard and GFCI receptacles. Works on GFI outlets and confirms operation of the ground fault protective device. Built to withstand a 6.6 ft. drop. Operating temp: 32 Degree to 140 Degree Fahrenheit. Nominal Voltage: 110/125V AC at 50/60Hz in 3 wire outlet.