Electrical outlets

So on one of my inspections I found that a few amount of electrical outlets seemed to be not tripping the 3 pronged tool I use to test them. The odd thing was that the outlets that didn’t trip my testing tool were adjacent to ones that did. Can i get opinions please?

Please include photos of your “testing tool” and the areas you are inquiring about.
You may also want to fill out you profile for the MB so folks know where you are and can give better advise based on the region.