Klein Tools Receptacle Testers are designed to detect the most common wiring problems in standard and GFCI receptacles. A convenient chart on the tester helps determine wiring condition in outlet, based on lights results. Conditions indicated: open ground, reverse polarity, open hot, open neutral, hot/ground reversed. Klein Tools Receptacle Testers are designed to detect the most common wiring problems in standard and GFCI receptacles. A convenient chart on the tester helps determine wiring condition in outlet, based on lights results. Conditions indicated: open ground, reverse polarity, open hot, open neutral, hot/ground reversed. GFCI Tester detects the most common wiring problems in standard and GFCI receptacles Operating temp: 32-Degree to 140-Degree Fahrenheit (0-Degree to 40-Degree Celsius) Klein Tools Receptacle Testers are designed to detect the most common wiring problems in standard and GFCI receptacles. A convenient chart on the tester helps determine wiring condition in outlet, based on lights results. Conditions indicated: open ground, reverse polarity, open hot, open neutral, hot/ground reversed.