New mobile digital devices raise new questions on architectural and urban design processes. They suggest new ways of dealing with projects in situ, organizing virtual and real data, acquiring information about shapes, materials, climate, lights, capturing specific genius loci of the site, as well as creating inter- actions between multiple stakeholders and users of urban areas. The set of available tools (smartphones, tablets, wearable devices, etc.) has not been yet deeply studied according to this prospect. How can these tools transform the understanding and the analysis of in situ environments? Modify design processes? Give shape or even create particular environments? The paper discusses these issues. It displays ideas for applications of mobile devices on architectural and urban design, wondering what such tools do change in our relationships to the city and to other people in everyday life. Lastly, it sees if the built environment can be affected by the effects of new digital mobility, especially focusing on the renewal of citizen participation process.