Skinput is a technology developed by Microsoft that uses the human body as an input surface for mobile devices. It projects virtual buttons and menus onto the skin using a pico-projector and detects taps and gestures using bio-acoustic sensors on an armband connected via Bluetooth. This allows for interaction without directly touching the mobile device, providing a new always-available input method. The document discusses the principles, working, advantages, and potential applications of Skinput as well as future areas of research.