A jeweler friend of mine makes this gorgeous product. In the "cage" is a piece of lava rock. Lava will absorb any fragrance or essential oil that you drop on it so it won't drip.
Simply stretch apart the cage and add a few drops off oil onto the lava rock. You can make it as strong as you like by adding more oil. It's not overpowering. It's a gentle smell that fills the car (especially when the heat is on).
You'll need to add drops about twice a week -- depending on how strong you like the smell.
If you want to switch scents, simply remove the rock and wash it with some warm, soapy water and let it dry out completely before adding another scent. You can get creative and blend your scents as well!
Check out our awesome selection of essential and fragrance oils you can use with this product.