Battery-operated automatic mist dispenser holds a can of special concentrated aerosol insecticide; sprays once every 15 minutes around the clock. Result: A continuous airborne "barrier" more effective in keeping flies out than regular manual spraying. Works well in enclosed areas such as milking parlors, workshops. Less effective in open spaces, but some report it definitely helps keep down flies in barn. One sprayer handles 6,000 cu. ft. of enclosed area. One can of insecticide lasts about a month. The Pyrethrin insecticide is approved for use in food processing rooms. Uses 2 size D batteries. Comes with one can of insecticide.