Well, you get what you pay for. It's cheap but useless. It showed every single outlet in my house as having an open ground. It also tripped every GFCI outlet as soon as I inserted it - i.e., before I pushed the GCFI Test button. For curiosity's sake, I gave it to a friend and asked her to try it at her house. Guess what? Every single outlet in her house shows as "open ground' as well, and it tripped every GFCI outlet just by being inserted into the outlet.
Do ourself a favor and do like I did - take the helpful advice offered in other reviews and pay a little more for the Sperry Instruments HGT6520,, which is a one-LED-per-condition product. I bought one after asking Amazon for a refund on this cheaper model The Sperry Instruments HGT6520 accurately indicated that my outlets were wired correctly, and the GFCI tester works as intended.