The document summarizes a research project that developed Skinput, a technique for using the human body as an input surface. A wearable armband containing piezoelectric sensors is used to capture vibrations from finger taps on the arm. The sensors are tuned to specific resonant frequencies to detect relevant low-frequency signals transmitted through soft tissues and bones. Machine learning classifiers analyze the acoustic features from the sensors to determine the location and timestamps of finger taps, allowing the arm to serve as a touch input surface. Initial proof-of-concept applications are demonstrated.