Alkyl also refers to an active ingredient in green algae preventatives used in swimming pools. In the U.S., condom advertising was legally restricted to their use as disease preventatives. Peanuts, then serve as tension preventatives. On Friday 13th, Pylon prepared preventatives for her house. An Ankh-Morpork tradesman, owner of "Sonky's Rubber Goods", and maker of "Sonky's Preventatives".