Stop Shock II 2 GFCI Outlet Tester, Easy To Test, Determine The Appropriate Wiring Correction Needed, Uses Advanced Circuitry & A Patent Pending Proprietary Design To Precisely Detect The Required Low Resistance, Less Than 10 Ohms, On Ground Wire, Provides A Clear & Easy To Understand Single LED Read Out Indication For Correct Wiring Without The Need To Memorize Or Decipher A Dual Indication Chart, Includes A GFCI Test Function To Test Outlets Wired In Parallel, High Impact ABS Housing With A 250 LB Crush Rating, Ability To Withstand Drops Of Up To 10'.