Systems and methods for location, motion, and contact detection and tracking in a portable networked device are disclosed. A portable device may include a motion detection unit including an accelerometer for detecting accelerations in one or more axes. Signals associated with the detected motion are processed to generate estimates of device acceleration, velocity, and relative and absolute locations. Additional processing may be performed to detect user gestures or other user input relevant to portable device control. Particular motion or vibrational characteristics may be also be detected and used by other processes in the portable device.