Combat dry air with your Optimus Cool Mist Ultrasonic Humidifier. Each cool mist humidifier includes a removable easy-to-fill transparent water tank with handle for easy filling. Each humidifier features an empty water auto shutoff switch and refill light that flashes when empty. This ultrasonic humidifier operates up to 18 hours on a full tank. It's constructed using antimicrobial-treated polymer plastic for lasting durability.