A second device configured to communicate with a first device, the second device comprising: a communication processor configured to communicate with the first device using a human-body communication method, wherein the second device sends and receives electromagnetic signals using a human body of a user as a transmission line for the electromagnetic signals; a motion sensor configured to detect a motion and to generate motion data representing the motion, wherein the motion is one of a motion of the second device and a motion of the first device; and circuitry configured to process instructions received from the first device, and a computer-readable memory, wherein the communication processor is configured to receive, from the first device, a first instruction indicating that the motion of the first device is the same as the motion of the second device; receive, from the first device, an identification code, and store the identification code in the computer-readable memory when the second device receives form the first device the identification code, wherein the circuitry is configured to: determine whether communication between the communication processor and the first device is terminated; and erase the identification code from the computer-readable memory when the communication between the communication processor and the first device is terminated. a communication processor configured to communicate with the first device using a human-body communication method, wherein the second device sends and receives electromagnetic signals using a human body of a user as a transmission line for the electromagnetic signals; a motion sensor configured to detect a motion and to generate motion data representing the motion, wherein the motion is one of a motion of the second device and a motion of the first device; and circuitry configured to process instructions received from the first device, and a computer-readable memory, wherein the communication processor is configured to receive, from the first device, a first instruction indicating that the motion of the first device is the same as the motion of the second device; receive, from the first device, an identification code, and store the identification code in the computer-readable memory when the second device receives form the first device the identification code, wherein the circuitry is configured to: determine whether communication between the communication processor and the first device is terminated; and erase the identification code from the computer-readable memory when the communication between the communication processor and the first device is terminated. process instructions received from the first device, and a computer-readable memory, wherein the communication processor is configured to receive, from the first device, a first instruction indicating that the motion of the first device is the same as the motion of the second device; receive, from the first device, an identification code, and store the identification code in the computer-readable memory when the second device receives form the first device the identification code, wherein the circuitry is configured to: determine whether communication between the communication processor and the first device is terminated; and erase the identification code from the computer-readable memory when the communication between the communication processor and the first device is terminated. determine whether communication between the communication processor and the first device is terminated; and erase the identification code from the computer-readable memory when the communication between the communication processor and the first device is terminated.