In the future, your smartphone will be able to sense your touch on its back for more complex interactions. Skin-On Interfaces is a project by Marc Teyssier, Gilles Bailly, Catherine Pelachaud, Eric Lecolinet, Andrew Conn and Anne Roudaut that explores such an approach. This artificial skin for robots and smartphones enables new forms of input gestures.
This approach enables tactile communication with robots. The above video shows how it all works.