Yankee Candle Smart Scent Vent Clip Odor Neutralizing Car Air Freshener, Macintosh (Pack of 4) Smart Scent Vent Clips have a clear window so you can easily see when a replacement unit is due The odor neutralizing unit fastens securely to any vehicle's dash vent A simple twist adjusts the level of fragrance to your personal preferences Provides up to 4 weeks of continuous fragrance