The Bionaire Ultrasonic Humidifier is energy efficient, filter-free, and ideal for small rooms within your home. The ultrasonic humidifier has a virtually silent operation and a 0.5-gallon water tank that propels cool, visible mist for up to 24 hours on its Low setting. The water tank contains antimicrobial protection to prevent mold and bacteria growth. This Bionaire humidifier uses high-frequency vibrations to humidify your room, and includes a water shortage indicator that illuminates when it's time to refill the tank. This portable humidifier is easy to move around your home. ULTRASONIC HUMIDIFIER: This energy-efficient ultrasonic humidifier propels visible, cool mist, with a virtually silent, filter-free operation 24-HOUR RUN TIME COOL-MIST HUMIDIFIER: Small humidifier has a 0.5-gallon-capacity water tank with a 24-hour run time on a full tank and Low setting ANTIMICROBIAL PROTECTION: Includes an antimicrobial protective material in the water tank to prevent mold and bacteria growth IDEAL SMALL SPACE HUMIDIFIER: Ideal for small rooms, plus its compact size allows for portability EASY TO USE: Includes 3 speed settings for optimal comfort levels, and one button control for easy operation REFILL LIGHT: Water shortage indicator illuminates when it's time to refill the tank Model: 2179548.