Now selected as a Wirecutter pick! Coway Airmega 200M, this four-stage filtration air purifier combines a pre-filter, an odorization filter, a true HEPA filter, and a bipolar device reduce contaminants in the air. The unit also employs a filter-change indicator, energy-saving eco mode, automatic speed control based on particles in the air, and an intuitive air quality indicator. The 200M can generate and maintain pure air in rooms up to 361 square feet, the size of a typical bedroom.