Method and apparatus for measuring body balance by wearable device

A wearable device comprises a communication module wirelessly communicating with a first external device, a motion sensor for sensing a user's motion, and a control unit. The wearable device collects first motion data generated by the user's motion and then transmits the collected data to the first external device, receives first security level data and second security level data from the first external device, and receives only the first security level data from the first external device when the wearable device is switched from a worn state to a removed state.