G&K Air Freshener System creates a clean/fresh environment with a consistent level of fragrance. Hydrogen forces a precise dose of fragrance, which natural air flow distributes throughout the room. Quiet operation and no moving parts or potential systems failures. No batteries required. One dispenser covers up to 6,000 cubic feet. SKU: 7857-544 8-week Service Cycle. SKU: 7857-558 12-week Service Cycle. US & Canada Colors: 655 Gray, 505 Black, 775 White. Use with G&K Air Freshener Dispenser Refill Cartridges - contemporary scents that contain only pure fragrances and contain Microtrans®, a true odor neutralizer: 439 Citrus, 729 Blue Splash, 748 Cucumber Melon, 534 Mango Blossom, 628 PURE™ Natural Odor Eliminator (odor neutralizer that leaves no residual scent). SKU: 7550-544 8-week Service Cycle. SKU: 7550-558 12-week Service Cycle.