Device, system and methods for using body worn sensors to analyze human body motion. The device, often configured to be worn on the user's wrist, arm, neck, belt or other location, comprises a processor, an output device (often a wireless transceiver), and at least one accelerometer, angle, location, direction, or physiological state sensor. The processor may be configured for various functions, such as analyzing habitual user activities, establishing normal baselines, classifying types of motion and reporting, and logging sensor readings or analysis results. Various algorithms may be used to determine when significant deviations from baseline values occur, and, depending on the type of deviation, the output device can transmit data and alerts. In some embodiments, the data and alerts may be further analyzed by other computerized devices such as mobile phones (smartphones), computers, internet servers, and the like.