Here is what the clever little device had to say. I got the same readings from different outlets in different parts of the house, except for one room which shows two green lights and no red whether or not the button is pressed.
Attached are two files, one of the line checker in action
So now the question is: What is my next step?
I did not look at the instructions, but I have used similar testers many times.
First note: The GFI fault tester button cannot perform its test function unless there is a ground circuit connected to the outlet. Without a ground, the test button just creates an oddball light pattern on the tester.
The single green light (when the test button is not
pressed) indicates the outlet has AC power, but there is no ground connection to the outlet. If there was
a ground connection, a second light would illuminate.
As anticipated, it appears your house is wired without grounding to the outlets. This is also what the UPS ‘wiring fault’ indicator is complaining about.
Next step? Well, if you wish to avail yourself of the additional safety and safeguards that a ground connection offers, somehow a proper ground wire needs to connect between the green screw on the back of the wall receptacle, and to an actual electrical ground point.
How this might be done would be specific to your house configuration, and to what the local electrical codes allow.