The key thing to remember is that when dealing with the metaphysical, often times it is our intent that becomes important. So if you use these items around your home with a specific intent (that it, to keep out the presence of certain entities), then that is what they are useful for.
Sacramentals are especially good in this role, because they have been blessed (I tend to think of them as being “irradiated” by God).
The real key, though, is to NOT think of “keeping the devil out”, because, in my experience, if we engage the Enemy in “spiritual warfare”, all we end up doing is attracting that same evil to ourselves. Rather, when I bless my house and walk the perimeter of my property with holy water, I am asking God to so fill my home and property with His presence and His love that nothing else can exist in the same space.
It was a little difficult for me to understand it at first myself, but after practicing this over the last few years, I have really noticed a difference in my home.