CHOOSE YOUR SCENT: Vent Scent 2 Pack comes with 10 unscented cotton sticks for any essential oil to be put on of your preference. LASTS TO YOUR LIKING: Replace the passive diffuser cotton sticks to extend smell or stop it to try different scents of your own. ZONING: Choose the whole area, room, or level of the home you'd like the freshener & place it on the nearest HVAC vent register. EASY INSTALL: Simply slide on a vent in the house you'd like the scent. No hassle of furnace filter openings. ADJUSTABLE STRENGTH: Alter the amount of oil and/or twist the device to adjust air to the scent. Support Small Business: Vent Scent is an American Owned and Operated Company.