Brittany is in a state of electricity dependency. To improve public awareness, energy consumers need to be able to access and understand their domestic energy consumption data. The present study deals with the design process of an innovative information appliance. These devices, if they manage to be intuitive and flexible, might facilitate behavior changes. The integration of an ergonomic follow-up associated to the system engineering processes is essential. The proposed contribution consists of an ergonomic approach to codesign a smart-grid information device through a simultaneous approach of these scientific fields. It leads to the creation of a device which goes beyond a simple transcript of information. With this, users can understand and analyze these data, it gives them the tools to modify their habits and save energy.