A peripheral device comprising: a data-producing element; a microcontroller coupled to the data-producing element to receive data generated by the data-producing element, the microcontroller being further configured to encode the data into an audio band signal; and an adder to combine the encoded data with audio signals on a microphone line, the adder being further configured to transfer the combined audio signals to a mobile device via a microphone conductor of an audio jack; an energy storage component coupled to the microphone conductor to be charged by a microphone bias voltage from the mobile device; a microphone coupled to the microphone bias voltage; and a select switch coupled to the energy storage component and the microphone, the select switch coupled to the microphone conductor of the audio jack, the select switch including a first switch position wherein data transmission via the microphone conductor is disabled and charging of the energy storage component using the microphone bias voltage via the microphone conductor is enabled, the select switch including a second switch position wherein data transmission via the microphone conductor is enabled and charging of the energy storage component using the microphone bias voltage via the microphone conductor is disabled; characterized in that the select switch is further coupled to an audio signal conductor of the audio jack; that in the first switch position, audio transmission via the microphone conductor is disabled, and that in the second switch position audio transmission via the microphone conductor is enabled; and that the peripheral device is operable to receive a switching tone from a mobile device to cause the select switch to toggle between the first position and the second position. a data-producing element; a microcontroller coupled to the data-producing element to receive data generated by the data-producing element, the microcontroller being further configured to encode the data into an audio band signal; and an adder to combine the encoded data with audio signals on a microphone line, the adder being further configured to transfer the combined audio signals to a mobile device via a microphone conductor of an audio jack; an energy storage component coupled to the microphone conductor to be charged by a microphone bias voltage from the mobile device; a microphone coupled to the microphone bias voltage; and a select switch coupled to the energy storage component and the microphone, the select switch coupled to the microphone conductor of the audio jack, the select switch including a first switch position wherein data transmission via the microphone conductor is disabled and charging of the energy storage component using the microphone bias voltage via the microphone conductor is enabled, the select switch including a second switch position wherein data transmission via the microphone conductor is enabled and charging of the energy storage component using the microphone bias voltage via the microphone conductor is disabled; characterized in that the select switch is further coupled to an audio signal conductor of the audio jack; that in the first switch position, audio transmission via the microphone conductor is disabled, and that in the second switch position audio transmission via the microphone conductor is enabled; and that the peripheral device is operable to receive a switching tone from a mobile device to cause the select switch to toggle between the first position and the second position.