A companion microphone for a hearing aid, comprising: a microphone; processing circuitry for producing an input signal from signals generated by the microphone; a wireless radio transmitter for transmitting the input signal to a wireless receiver of the hearing aid; an accelerometer; a battery and power control circuitry; and, wherein the processing circuitry is configured to adjust the radio transmission power of the wireless transmitter in dependence upon signals generated by the accelerometer, wherein the processing circuitry is configured to determine a device state from the accelerometer signals and set the radio transmission power level according to the device state, and wherein the processing circuitry is further configured to: determine a device state from the accelerometer signals, wherein the device state includes an orientation of the companion microphone relative to gravity and whether or not the companion microphone is moving; set the radio transmission power level at a high power level if the device state indicates that the companion microphone is moving; set the radio transmission power level at a high power level if the device state indicates that the companion microphone has an orientation that corresponds to how the companion microphone would be oriented when worn by a user sitting or standing upright; and, set the radio transmission power level at a low power level if the device state indicates that the companion microphone has an orientation that corresponds to how the companion microphone would be oriented when placed upon a stationary structure and no movement is detected. a microphone; processing circuitry for producing an input signal from signals generated by the microphone; a wireless radio transmitter for transmitting the input signal to a wireless receiver of the hearing aid; an accelerometer; a battery and power control circuitry; and, wherein the processing circuitry is configured to adjust the radio transmission power of the wireless transmitter in dependence upon signals generated by the accelerometer, wherein the processing circuitry is configured to determine a device state from the accelerometer signals and set the radio transmission power level according to the device state, and wherein the processing circuitry is further configured to: determine a device state from the accelerometer signals, wherein the device state includes an orientation of the companion microphone relative to gravity and whether or not the companion microphone is moving; set the radio transmission power level at a high power level if the device state indicates that the companion microphone is moving; set the radio transmission power level at a high power level if the device state indicates that the companion microphone has an orientation that corresponds to how the companion microphone would be oriented when worn by a user sitting or standing upright; and, set the radio transmission power level at a low power level if the device state indicates that the companion microphone has an orientation that corresponds to how the companion microphone would be oriented when placed upon a stationary structure and no movement is detected. determine a device state from the accelerometer signals, wherein the device state includes an orientation of the companion microphone relative to gravity and whether or not the companion microphone is moving; set the radio transmission power level at a high power level if the device state indicates that the companion microphone is moving; set the radio transmission power level at a high power level if the device state indicates that the companion microphone has an orientation that corresponds to how the companion microphone would be oriented when worn by a user sitting or standing upright; and, set the radio transmission power level at a low power level if the device state indicates that the companion microphone has an orientation that corresponds to how the companion microphone would be oriented when placed upon a stationary structure and no movement is detected.