Drop a few drops of essential oil or perfume on the felt and enjoy the wonderful scent.
(in the second photo it is the first pendant)

Color of the felt varies per necklace. You can specify a preference, but this does not guarantee that it will be present. Tip: You could buy a piece of felt at the craft store and cut out circles the size of the pendant. This way you immediately have several in stock to change scents more quickly if you wish.