Each locket-style necklace comes with three inserts (either leather or felt, depending on the piece) that you put into the locket. You can put 1-3 drops of an essential oil of your choice on the insert, and depending on the oil, you may be able to smell it for up to a week. Once the scent is gone, feel free to choose a different oil to use (or mix them if you want - that's fine too!). You can reuse the inserts over and over.
For jewelry with lava stones, you can put a drop of oil directly on these porous beads and the scent will also last for a couple of days. Just reapply an oil when the scent is gone!