A terminal device configured to be used with a master wireless device, the terminal device comprising: an activator; a power generator that generates electric charge in response to operation of the activator; an electric storage part that stores the electric charge; a voltage converter that converts a first voltage obtained from the electric storage part into a second voltage; a control circuit including a first input unit, a second input unit, an output unit, a nonvolatile memory, and a signal processing circuit, the control unit being operable to start operating from a first time with the second voltage as a power source that is applied to the first input unit, and stop operating at a second time at which the second voltage falls below a lower limit voltage value; and a wireless circuit that transmits an output signal from the output unit by radio, characterized by a voltage detector that outputs, to the second input unit, an output value in accordance with the first voltage, wherein the control circuit further includes an oscillator that generates a clock and a timer that measures a time during operation of the control circuit based on the clock, wherein the control circuit configured to determine registration data based on the time measured by the timer, wherein, when an m-th activation starts, the nonvolatile memory stores first to (m-1)-th pieces of registration data that are obtained while the activator; is activated first to (m-1)-th times, respectively, wherein, when the output value exceeds a predetermined first threshold at a third time after the first time during the m-th activation, the control circuit is configured to: start to measure a time after the third time; store, in the nonvolatile memory by the second time, the m-th registration data determined during the m-th activation based on the time measured by the timer; and output either a pairing mode signal or a normal mode signal as the output signal from the output unit according to the first to (m-1)-th pieces of registration data or according to the first to (m-1)-th pieces of registration data and the m-th registration data, and wherein the terminal device and the master wireless device are paired with each other in response to the pairing mode signal output from the terminal device. an activator; a power generator that generates electric charge in response to operation of the activator; an electric storage part that stores the electric charge; a voltage converter that converts a first voltage obtained from the electric storage part into a second voltage; a control circuit including a first input unit, a second input unit, an output unit, a nonvolatile memory, and a signal processing circuit, the control unit being operable to start operating from a first time with the second voltage as a power source that is applied to the first input unit, and stop operating at a second time at which the second voltage falls below a lower limit voltage value; and start operating from a first time with the second voltage as a power source that is applied to the first input unit, and stop operating at a second time at which the second voltage falls below a lower limit voltage value; and a wireless circuit that transmits an output signal from the output unit by radio, characterized by a voltage detector that outputs, to the second input unit, an output value in accordance with the first voltage, wherein the control circuit further includes an oscillator that generates a clock and a timer that measures a time during operation of the control circuit based on the clock, wherein the control circuit configured to determine registration data based on the time measured by the timer, wherein, when an m-th activation starts, the nonvolatile memory stores first to (m-1)-th pieces of registration data that are obtained while the activator; is activated first to (m-1)-th times, respectively, wherein, when the output value exceeds a predetermined first threshold at a third time after the first time during the m-th activation, the control circuit is configured to: start to measure a time after the third time; store, in the nonvolatile memory by the second time, the m-th registration data determined during the m-th activation based on the time measured by the timer; and output either a pairing mode signal or a normal mode signal as the output signal from the output unit according to the first to (m-1)-th pieces of registration data or according to the first to (m-1)-th pieces of registration data and the m-th registration data, and start to measure a time after the third time; store, in the nonvolatile memory by the second time, the m-th registration data determined during the m-th activation based on the time measured by the timer; and output either a pairing mode signal or a normal mode signal as the output signal from the output unit according to the first to (m-1)-th pieces of registration data or according to the first to (m-1)-th pieces of registration data and the m-th registration data, and wherein the terminal device and the master wireless device are paired with each other in response to the pairing mode signal output from the terminal device.