1. A method comprising: by a computing device, determining one or more sensor signals detected by one or more sensors of the computing device, the sensor signals being indicative of motion of the computing device; by the computing device, selecting one of a plurality of activity categories that corresponds to a portion of the sensor signals, wherein each of the activity categories comprises one or more activity types and is characterized by a motion that the activity types in the selected activity category have in common; by the computing device, determining one of the activity types in the selected activity category by: analyzing the sensor signals with respect to each of the activity types in the selected activity category; and calculating a probability of each of the activity types based on the analysis; and by the computing device, displaying the determined activity type on a display of the computing device.