Fragrance cassette is designed for use with Rubbermaid 9C90 Fan System (sold separately). Gel absorbs odors in the air and converts them to nontoxic, odorless compounds for long-lasting odor control for restrooms, hospitals, nursing homes and commercial buildings. Gel dissolves as it's used to give a visual cue to replace. Fragrance cassette provides consistent refreshing fragrance release for 24 hours a day over a 30-day period. Patented, see-through fragrance cassette canister includes a battery for easy one-step replacement.