The Gardner Bender GFCI Outlet Tester was ergonomically designed for today's electrical professional. This unit plugs into any standard 120-Volt outlet and indicates the wiring condition of the outlet. The GFI-3501 also has the ability to test any outlet protected by a ground fault receptacle to ensure proper interruption operation. With charts on both sides of the unit, any user can quickly identify which of the six wiring conditions is indicated by the integrated neon lamps. Test any GFCI outlet, standard outlet, or extension cord.