A standard outlet tester - great construction and made by a top name brand - GB (Gardner Bender). With the bonus of a GFCI (ground fault circuit interrupter) test button. The GFCI test button allows you to see if an outlet is protected by a nearby ground fault circuit interrupter. Sometimes GFCIs are far away - such as in the panel box or near the panel box. So you can test any outlet to see if it is protected or not.
Primarily these are used in EMF to test if an outlet is wired correctly and if it has a ground. These sort of outlet testers can't find all wiring errors. But one of the important ones is to see if an outlet's ground is connected, or if it is "Open Ground" - meaning the ground is not hooked up to a grounding equipment conductor (green or bare ground wire). This is an issue that can cause large, unwanted electrical fields, as well as very real potential safety issues. Many grounded appliances and tools depend on a ground for safety, to prevent the metal body of the appliance or device from becoming energized and electrocuting someone!
Test your outlets for safety and health with this handy, inexpensive, reliable tester.