We present Skinput, a technology that appropriates the hu- man body for acoustic transmission, allowing the skin to be used as an input surface. In particular, we resolve the loca- tion of finger taps on the arm and hand by analyzing me- chanical vibrations that propagate through the body. We collect these signals using a novel array of sensors worn as an armband. This approach provides an always available, naturally portable, and on-body finger input system. We assess the capabilities, accuracy and limitations of our tech- nique through a two-part, twenty-participant user study. To further illustrate the utility of our approach, we conclude with several proof-of-concept applications we developed.