What does this patent actually cover? If there is a key holder with a completely different design etc. but the same theory does that infringe? I mean does the look/design just have to be different or what?
The cited patent is a design patent. Design patents cover the ornamental design of a functional object. Thus, the specific function is not covered by patent, but you should avoid making a product that looks like what is shown in the patent's figures. If your key holder is truly a "completely different design", it is likely fine with respect to this patent even if it functions similarly. There is a gray area regarding whether similar products look similar enough to infringe on design patents so you may want to consult with an expert before going to market. As always, I caution that the fact that you may avoid infringement of this particular design patent doesn't mean there isn't some other relevant patent art that you need to make yourself aware of.