NOW® Solutions Ultrasonic USB Oil Diffuser unites aromatherapy with modern scientific innovation to create a diffuser that plugs into your laptop with a USB cable. This mobile diffuser is BPA-free and diffuses essential oils for up to 4 hours. It utilizes high-frequency ultrasonic electrical vibrations to create an ultra-fine mist. This diffusion method doesn't utilize heat, which maintains essential oil integrity and holistic properties every time you use it. Just add 70 ml (2.37 fl. oz.) of water and 5 drops of your favorite essential oils and enjoy. When it's out of water it automatically shuts off.