The SpaScenter electric diffuser uses a fan to diffuse your essential oils into the air. Plugs into a regular 110v outlet. Essential oils are placed onto cotton pads. The Aroma Shell is also electric and has a small metal bowl (removable) in which you place your essential oils. Plugs into a regular 110v outlet. The bowl is heated to diffuse your essential oils. The Scent Ball plugs into a regular 110v outlet and it heats a cotton pad containing your essential oils to diffuse them into the air. The Mio battery powered fan diffuser is portable and ideal for work, travel, and bedside use. The Car Scenter plugs into your car's lighter outlet. Extra refill pads for all diffusers is included.