Unlike other humidifiers that grow slimy mold and mildew on the water tank surface, the Guardian Technologies Pure Guardian H4500 144 Hour Ultrasonic Humidifier uses Silver Clean?technology to fight the growth of mold and mildew on the surface of the water tank. Thanks to ultrasonic technology it is ultra-quiet when it runs making it ideal to have on while you sleep. The humidifier is equipped with the option for warm or cool mist and a low water indicator light lets you know when it's time to refill the water tank. Also features a soft glow night light, as well as a digital display. If you want to keep your baby happy and satisfied, then the Pure Guardian H4500 144 Hour Ultrasonic Humidifier is the humidifier that you need.