OK, in my basement I have 2-prong plug-ins. Everything works fine with them. I guess you'd have to say they are open ground since they are not 3-prong plug-ins, right? (My house was built in 1957 BTW.) I do plug in to them via GFI strips anyway. Anyway, I guess I should get testers for both 2-prong AND 3-prong plug-ins as there are a few of those around here too (3'ers), not to mention for testing places you may play at. So...here are 2 for consideration: I am a bit confused in that the 3501 model is ONLY for GFCI outlets like you might find in a bathroom right? 1. Gardner Bender GFI-3501 GFCI Outlet Tester (3-prong): Product Features Tests ground fault receptacles by overloading circuit and tripping GFCI Easy to use Tests for seven conditions Succession of yellow and red lights provides indications of circuit status or specifies wiring errors Tester trips GFCI between 6-9 mA http://www.amazon.com/ 2.Gardner Bender GFI-501A Ground Fault Receptacle Tester and Circuit Analyzer (2 -prong) Product Features Professional grade ground fault receptacle tester Easy-to-read red and yellow light system Protected by a ground fault receptacle Tester trips GFCI between 6- 9 mA 1-year limited manufacturer's warranty http://www.amazon.com/Gardner-GFI-501A-Receptacle-Circuit-Analyzer/dp/B00004WLJM I also am wondering if it is not just more handy to bring a GFI strip to plug into at anyplace you play anyway. What say the electro-whizzes here?