An apparatus comprising: transmitter means for providing an amplitude modulated signal via a transmitting electrode means to a body to which the transmitting electrode means is configured to be applied, wherein the transmitter means further comprises modulator means configured to modulate an amplitude of a first signal, being a plurality of pulses, in accordance with an amplitude modulation waveform to generate an amplitude modulated signal for which amplitude modulation is repeated at a predefined frequency, the amplitude modulated signal being in the form of an amplitude modulated pulse train; and receiver means for receiving signals, responsive to the amplitude modulated signal, via a receiving electrode means that is configured to be applied to the body and to be remote from the transmitting electrode means so as to be in wireless communication with the transmitting electrode means via the body, the receiver means being configured to process the received signals to determine a measure of a body impedance; wherein the receiver means comprises: comparator means configured to compare the received signals to a threshold level in order to generate a rectangular output waveform having the predefined frequency, wherein the rectangular output waveform has a duty cycle that is indicative of the measure of the body impedance; and processor means configured to determine the measure of the body impedance based on upon a predefined relationship between duty cycle and body impedance, wherein the predefined relationship is stored in a lookup table of a memory device and is identified based on correlating duty cycles of rectangular output waveforms to known measures of body impedance for multiple subjects. transmitter means for providing an amplitude modulated signal via a transmitting electrode means to a body to which the transmitting electrode means is configured to be applied, wherein the transmitter means further comprises modulator means configured to modulate an amplitude of a first signal, being a plurality of pulses, in accordance with an amplitude modulation waveform to generate an amplitude modulated signal for which amplitude modulation is repeated at a predefined frequency, the amplitude modulated signal being in the form of an amplitude modulated pulse train; and receiver means for receiving signals, responsive to the amplitude modulated signal, via a receiving electrode means that is configured to be applied to the body and to be remote from the transmitting electrode means so as to be in wireless communication with the transmitting electrode means via the body, the receiver means being configured to process the received signals to determine a measure of a body impedance; wherein the receiver means comprises: comparator means configured to compare the received signals to a threshold level in order to generate a rectangular output waveform having the predefined frequency, wherein the rectangular output waveform has a duty cycle that is indicative of the measure of the body impedance; and processor means configured to determine the measure of the body impedance based on upon a predefined relationship between duty cycle and body impedance, wherein the predefined relationship is stored in a lookup table of a memory device and is identified based on correlating duty cycles of rectangular output waveforms to known measures of body impedance for multiple subjects. comparator means configured to compare the received signals to a threshold level in order to generate a rectangular output waveform having the predefined frequency, wherein the rectangular output waveform has a duty cycle that is indicative of the measure of the body impedance; and processor means configured to determine the measure of the body impedance based on upon a predefined relationship between duty cycle and body impedance, wherein the predefined relationship is stored in a lookup table of a memory device and is identified based on correlating duty cycles of rectangular output waveforms to known measures of body impedance for multiple subjects.