Purchase a receptacle tester that has GFCI testing capability. Not all testers will indicate GFCI status, so check the package. Plug tester into the receptacle, just as you would plug in an appliance.

That's where devices like the Klein Tools RT250 GFCI Outlet Tester come in handy. These pocket-sized, battery-operated tools can expose red flags not visible to the naked eye, saving time ...

The concept of an outlet tester is pretty simple: plug the gadget into a suspect wall receptacle, and an array of LEDs light up in various patterns to alert the user to any wiring faults.