In one example, a method includes determining, by a processor operating in a first power mode and based on first motion data, a first activity of a user, transitioning from operating in the first power mode to operating in a second power mode, wherein the processor consumes less power while operating in the second power mode than in the first power mode, responsive to determining, while the processor is operating in the second power mode and based on second motion data, that a change in an angle relative to gravity satisfies a threshold, transitioning from operating in the second power mode to operating in the first power mode, determining, by the processor and based on second motion data, a second activity of the user, and, responsive to determining that the second activity is different from the first activity, performing an action.