Klein Tools RT210 Receptacle GFCI 3 Wire Tester detects common wiring problems in standard and GFCI receptacles. The Klein Tools RT210 indicates open ground, reverse polarity, wiring correct, hot/ground reversed, open neutral, open hot, and features bright LEDs with a color key code on the unit. The Klein Tools RT210 is an economical and effective receptacle tester that works on both standard and GFCI receptacles.