My research is based on the observation that the miniaturization of mobile devices has come to a halt, because input controls have to be large enough to be operated. However, this halt is not due to hardware limitations. I believe that further miniaturization and thus true ubiquity of mobile devices requires a better understanding of human factors. In my research, I investigate and leverage human mental models to create ultra-small touch devices. I also build systems that allow users to interact spatially in the empty space in front of them, the ground they stand on, and on their skin. My tools include the combination of software and hardware, prototyping, and depth cameras.