Witches bells are believed that loud sounds, like those from bells or chimes scare off ghosts and demonic entities. Not just the iron from which the bells are made has a cleansing, protective effect, it is also the purifying sound waves, ringing through the air that ward off the evil.
You can hang it outside of your front and back doors or inside by your front and back. I recommend outside!
These are handmade and ritualized. Prepared and all you have to do is hang it.