A test method for testing a piezoelectric gas sensor device , the method comprising: providing a self-test circuit module, STCM, adapted to couple to an output port of a piezoelectric Unit Under Test, PZ-UUT, ; receiving an output signal from the PZ-UUT in response to the PZ-UUT being stimulated by an excitation signal , the excitation signal being obtained by (a) injecting excitation energy to the PZ-UUT during a first time-interval (T1), and (b) supplying substantially no excitation energy to the PZ-UUT during a second time-interval (T2) immediately subsequent to the first time-interval (T1); determining, with the STCM , the amplitude of a frequency content of the received output signal during the second time-interval (T2); comparing, with the STCM , the determined amplitude of the frequency content at a predetermined comparison time during the second time-interval (T2) to a predetermined threshold amplitude ; if the determined amplitude of the frequency content is less than the predetermined threshold amplitude , then generating a status signal indicative of a fault in the PZ-UUT ; wherein the value of the predetermined threshold amplitude accepts good gas sensor devices with an acceptable time-domain response signal which follows a damped natural frequency of the piezoelectric element and fails bad gas sensor devices with an unacceptable time-domain response signal which drops to substantially zero within a time determined by a damping function having a time constant of less than about 50% of the second time-interval (T2) providing a self-test circuit module, STCM, adapted to couple to an output port of a piezoelectric Unit Under Test, PZ-UUT, ; receiving an output signal from the PZ-UUT in response to the PZ-UUT being stimulated by an excitation signal , the excitation signal being obtained by (a) injecting excitation energy to the PZ-UUT during a first time-interval (T1), and (b) supplying substantially no excitation energy to the PZ-UUT during a second time-interval (T2) immediately subsequent to the first time-interval (T1); (a) injecting excitation energy to the PZ-UUT during a first time-interval (T1), and (b) supplying substantially no excitation energy to the PZ-UUT during a second time-interval (T2) immediately subsequent to the first time-interval (T1); determining, with the STCM , the amplitude of a frequency content of the received output signal during the second time-interval (T2); comparing, with the STCM , the determined amplitude of the frequency content at a predetermined comparison time during the second time-interval (T2) to a predetermined threshold amplitude ; if the determined amplitude of the frequency content is less than the predetermined threshold amplitude , then generating a status signal indicative of a fault in the PZ-UUT ; wherein the value of the predetermined threshold amplitude accepts good gas sensor devices with an acceptable time-domain response signal which follows a damped natural frequency of the piezoelectric element and fails bad gas sensor devices with an unacceptable time-domain response signal which drops to substantially zero within a time determined by a damping function having a time constant of less than about 50% of the second time-interval (T2) <EOS>