1. A command input method using a three dimensional inertia based motion recognition device (MRD) coupled to a host interface device (HID), the method comprising: wearing the MRD as a ring; transmitting signals from the MRD to the host interface device (HID) wherein the transmitted signals correspond to three-dimensional inertia changes of the MRD; detecting a level of the transmitted signals; determining that the MRD is substantially motionless when the detected level of the transmitted signals is below a predetermined threshold level; detecting an initial posture of the MRD when the MRD is sensed to be substantially motionless; determining that the MRD is in motion when the detected level of the transmitted signals is above the predetermined threshold level; using the transmitted signals that are determined to be above the predetermined threshold level to determine a pattern of movement of the MRD; determining by the HID a final input command based on the combination of the detected initial posture and the determined pattern of the movement of the MRD, wherein the determining uses a mapping table that stores final input commands designated by the combination of the detected initial posture and the determined pattern of the movement of the MRD.