Harmony Pet Home Diffuser Refills for Cats are unplugged. Contains 2 refill cartridge. Each diffuser refill continually releases a safe pheromone for cats for up to 30 days, providing 1 month of calming benefits when they need it the most. The P.E.T. pheromone mimics the maternal pheromone from momma cat to soothe her kittens. Cats of all ages recognize this calming pheromone for life.