Abstract: A method of monitoring a subject (7) in a vehicle seat (6), the method including: a) acquiring a target signal from the subject with a piezoelectric transducer (1) provided in or on the vehicle seat; b) processing the target signal to extract a cardiac signal (24) and/or a respiratory signal (25); and c) outputting the cardiac and/or respiratory signal. A method of monitoring a subject including: a) acquiring a target signal from the subject; b) bandpass filtering (27) the target signal in accordance with a set of cardiac filter coefficients to extract a cardiac signal (24); c) bandpass filtering (30) the target signal in accordance with a set of respiratory filter coefficients to extract a respiratory signal (25); d) adapting (29, 33) the set of cardiac filter coefficients so as to reduce artefacts in the cardiac signal; e) adapting (50, 32) the set of respiratory filter coefficients so as to reduce artefacts in the respiratory signal; and f) outputting the cardiac and respiratory signal signals.