A sensor device comprising: a sensor unit configured to directly or indirectly detect sensing data indicating a motion and an orientation of a hitting tool ; a communication unit configured to transmit the sensing data detected by the sensor unit to an external device ; a control unit configured to control operation of the sensor unit and the communication unit ; a main memory configured to contain information obtained by the sensor unit and to retain information without electric power supplied; and a temporary storage memory configured to temporarily store the sensing data detected by the sensor unit in an electric power saving mode; wherein the control unit or the sensor unit changes at least one of the sensor unit and the control unit to the electric power saving mode, upon detecting that the hitting tool has a specific orientation for a certain amount of time; characterised in that the control unit or the sensor unit changes at least one of the sensor unit and the control unit from a normal mode to the electric power saving mode, upon detecting that the hitting tool has a predefined orientation facing in the gravity force direction for a certain amount of time; wherein the sensing data that is temporarily stored in the temporary storage memory is supplied from the temporary storage memory to the control unit when the control unit changes from the electric power saving mode to the normal mode; wherein the sensor unit acquires the sensing data at a predetermined sampling rate in the case of the normal mode and at a reduced sampling rate in the case of the electric power saving mode, wherein the reduced sampling rate is lower than the predetermined sampling rate; and wherein no electric power is supplied to the main memory in the electric power saving mode. a sensor unit configured to directly or indirectly detect sensing data indicating a motion and an orientation of a hitting tool ; a communication unit configured to transmit the sensing data detected by the sensor unit to an external device ; a control unit configured to control operation of the sensor unit and the communication unit ; a main memory configured to contain information obtained by the sensor unit and to retain information without electric power supplied; and a temporary storage memory configured to temporarily store the sensing data detected by the sensor unit in an electric power saving mode; wherein the control unit or the sensor unit changes at least one of the sensor unit and the control unit to the electric power saving mode, upon detecting that the hitting tool has a specific orientation for a certain amount of time; characterised in that the control unit or the sensor unit changes at least one of the sensor unit and the control unit from a normal mode to the electric power saving mode, upon detecting that the hitting tool has a predefined orientation facing in the gravity force direction for a certain amount of time; wherein the sensing data that is temporarily stored in the temporary storage memory is supplied from the temporary storage memory to the control unit when the control unit changes from the electric power saving mode to the normal mode; wherein the sensor unit acquires the sensing data at a predetermined sampling rate in the case of the normal mode and at a reduced sampling rate in the case of the electric power saving mode, wherein the reduced sampling rate is lower than the predetermined sampling rate; and wherein no electric power is supplied to the main memory in the electric power saving mode. <EOS>