Scent Free Cartridge exclusively for cat-safe, hygienic cleaning of the CatGenie 120 self-washing cat box (1 Cartridge good for 120 Cleanings or 240 Cleanings when you CatGenie 120 is on Cat Activation). The 120 Cartridge only works in the CatGenie 120 Model. The 120 Cartridge (clear) will NOT work in the original CatGenie, which only uses the 60 Cartridge (green) The 60 Cartridge will NOT work in the CatGenie 120.