A system for evaluating a toxic gas electrochemical sensor, the system comprising: a potentiostat circuit electrically connected to the toxic gas electrochemical sensor; a voltage waveform generator connected to the potentiostat circuit and enabled to apply a voltage sine wave at a plurality of selected frequencies to a reference electrode of the toxic gas electrochemical sensor; a current measurement circuit electrically connected to the toxic gas electrochemical sensor for measuring an amplitude and a phase of a current through the toxic gas electrochemical sensor in response to the applied voltage sine wave; and a microcontroller electrically connected to the voltage waveform generator and the current measurement circuit, wherein the microcontroller controls the voltage waveform generator, receives a corresponding output from the current measurement circuit indicative of the amplitude and the phase of the current through the toxic gas electrochemical sensor at each of the plurality of selected frequencies, and characterised in that the microcontroller analyzes the output from the current measurement circuit to determine information about a response time of the toxic gas electrochemical sensor, wherein analyzing the output comprises calculating a real impedance and an imaginary impedance corresponding to a current measurement at each of the plurality of selected frequencies resulting in calculated real impedances and calculated imaginary impedances, and wherein analyzing the output further comprises comparing a Nyquist plot of the calculated real impedances and the calculated imaginary impedances with a corresponding reference Nyquist plot of reference real impedances and reference imaginary impedances wherein the comparing the Nyquist plot with the corresponding reference Nyquist plot includes evaluating differences in a location of one or more features of the Nyquist plot with a location of a corresponding one or more features of the reference Nyquist plot, the corresponding features including a diameter of a half circle formed by a plot of the reference impedances in the reference Nyquist plot, wherein if a diameter of a half circle formed by a plot of the calculated impedances in the Nyquist plot is greater than the diameter of the half circle formed by the plot of the reference impedances in the reference Nyquist plot, the microcontroller determines that an effective polarization impedance of the toxic gas electrochemical sensor has increased and that the response time has increased. a potentiostat circuit electrically connected to the toxic gas electrochemical sensor; a voltage waveform generator connected to the potentiostat circuit and enabled to apply a voltage sine wave at a plurality of selected frequencies to a reference electrode of the toxic gas electrochemical sensor; a current measurement circuit electrically connected to the toxic gas electrochemical sensor for measuring an amplitude and a phase of a current through the toxic gas electrochemical sensor in response to the applied voltage sine wave; and a microcontroller electrically connected to the voltage waveform generator and the current measurement circuit, wherein the microcontroller controls the voltage waveform generator, receives a corresponding output from the current measurement circuit indicative of the amplitude and the phase of the current through the toxic gas electrochemical sensor at each of the plurality of selected frequencies, and characterised in that the microcontroller analyzes the output from the current measurement circuit to determine information about a response time of the toxic gas electrochemical sensor, wherein analyzing the output comprises calculating a real impedance and an imaginary impedance corresponding to a current measurement at each of the plurality of selected frequencies resulting in calculated real impedances and calculated imaginary impedances, and wherein analyzing the output further comprises comparing a Nyquist plot of the calculated real impedances and the calculated imaginary impedances with a corresponding reference Nyquist plot of reference real impedances and reference imaginary impedances wherein the comparing the Nyquist plot with the corresponding reference Nyquist plot includes evaluating differences in a location of one or more features of the Nyquist plot with a location of a corresponding one or more features of the reference Nyquist plot, the corresponding features including a diameter of a half circle formed by a plot of the reference impedances in the reference Nyquist plot, wherein if a diameter of a half circle formed by a plot of the calculated impedances in the Nyquist plot is greater than the diameter of the half circle formed by the plot of the reference impedances in the reference Nyquist plot, the microcontroller determines that an effective polarization impedance of the toxic gas electrochemical sensor has increased and that the response time has increased.