The Klein Tools RT250 GFCI Outlet Tester is a top circuit breaker tester, earning a 4.8-star rating from nearly 10,000 global users. Priced at $22, it is an important device for testing wiring ...

The latter is similar to the Outlet Tester described further down in this list, with a plug that connects to a standard GFCI ...

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.