A method of operating a gas sensing device, wherein the gas sensing device comprises: - a gas sensor circuit comprising a resistive gas sensing element and a resistive heater, and - a control circuit coupled to the gas sensor circuit, the method comprising: - receiving at the control circuit a signal from the gas sensor circuit, said signal being indicative of a value of resistance of said resistive gas sensing element; - processing said signal received from the gas sensor circuit to compute a value of a gas concentration; - performing a comparison of said value of gas concentration to a certain threshold value and setting the gas sensing device to an alert signal issue state as a function of the outcome of said comparison, wherein setting the gas sensing device to said alert signal issue state is conditioned on the outcome of a diagnosis procedure, the diagnosis procedure comprising: - applying a current pulse (I 1, I 2) to said resistive heater; - sensing said signal received from the gas sensor circuit as a result of application of said current pulse (I 1); - computing, as a function of said signal received, a value of resistance of said resistive gas sensing element and a value of slope of said signal received; - classifying the gas sensor circuit as a function of said value of resistance of said resistive gas sensing element and said value of slope of said signal received, in one of a first class, a second class and a third class indicative of the gas sensor circuit being faulty, degraded or correctly operating, respectively; and i) as a result of the gas sensor circuit being classified in said first class, disabling setting the gas sensing device to said alert signal issue state; ii) as a result of the gas sensor circuit being classified in said second class, triggering a sensitivity correction procedure of the gas sensor circuit and repeating said diagnosis procedure; and iii) as a result of the gas sensor circuit being classified in said third class, enabling setting the gas sensing device to said alert signal issue state. - a gas sensor circuit comprising a resistive gas sensing element and a resistive heater, and - a control circuit coupled to the gas sensor circuit, - receiving at the control circuit a signal from the gas sensor circuit, said signal being indicative of a value of resistance of said resistive gas sensing element; - processing said signal received from the gas sensor circuit to compute a value of a gas concentration; - performing a comparison of said value of gas concentration to a certain threshold value and setting the gas sensing device to an alert signal issue state as a function of the outcome of said comparison, wherein setting the gas sensing device to said alert signal issue state is conditioned on the outcome of a diagnosis procedure, the diagnosis procedure comprising: - applying a current pulse (I 1, I 2) to said resistive heater; - sensing said signal received from the gas sensor circuit as a result of application of said current pulse (I 1); - computing, as a function of said signal received, a value of resistance of said resistive gas sensing element and a value of slope of said signal received; - classifying the gas sensor circuit as a function of said value of resistance of said resistive gas sensing element and said value of slope of said signal received, in one of a first class, a second class and a third class indicative of the gas sensor circuit being faulty, degraded or correctly operating, respectively; and i) as a result of the gas sensor circuit being classified in said first class, disabling setting the gas sensing device to said alert signal issue state; ii) as a result of the gas sensor circuit being classified in said second class, triggering a sensitivity correction procedure of the gas sensor circuit and repeating said diagnosis procedure; and iii) as a result of the gas sensor circuit being classified in said third class, enabling setting the gas sensing device to said alert signal issue state. - applying a current pulse (I 1, I 2) to said resistive heater; - sensing said signal received from the gas sensor circuit as a result of application of said current pulse (I 1); - computing, as a function of said signal received, a value of resistance of said resistive gas sensing element and a value of slope of said signal received; - classifying the gas sensor circuit as a function of said value of resistance of said resistive gas sensing element and said value of slope of said signal received, in one of a first class, a second class and a third class indicative of the gas sensor circuit being faulty, degraded or correctly operating, respectively; and i) as a result of the gas sensor circuit being classified in said first class, disabling setting the gas sensing device to said alert signal issue state; ii) as a result of the gas sensor circuit being classified in said second class, triggering a sensitivity correction procedure of the gas sensor circuit and repeating said diagnosis procedure; and iii) as a result of the gas sensor circuit being classified in said third class, enabling setting the gas sensing device to said alert signal issue state. i) as a result of the gas sensor circuit being classified in said first class, disabling setting the gas sensing device to said alert signal issue state; ii) as a result of the gas sensor circuit being classified in said second class, triggering a sensitivity correction procedure of the gas sensor circuit and repeating said diagnosis procedure; and iii) as a result of the gas sensor circuit being classified in said third class, enabling setting the gas sensing device to said alert signal issue state.