I bought this to hang on my doorknob (inside) so I can hear the door open and close...works great and looks pretty.
The hanging loop is a little small for a standard doorknob as it was meant to be a mobile or wind chime to hang on a hook, so I just use a ribbon of my own, to tie it on the doorknob.
These were purchased for family. We always add an ornament to the outside of their packages. They love this tradition, so every year they have something new for their Christmas tree.