The response ( res) and recovery ( recov) time are also an impor- tant factor to evaluate the gas sensing properties of the sensor. Rapid response and recovery to a tested gas are required for practical application. Fig. 6 displays the response and recovery characteristics of the as-prepared composite to 100 ppm methanol. The results indicate that the sensor immediately responded when methanol gas was introduced and then rapidly recovered to its ini- tial value after the methanol was released. The response time ( res ) and recovery time ( recov ) of the SnO2 -Pd-Pt-In2 O3 composite sen- sor are about 32 s and 47 s, respectively. It is found that the response and recovery rate are ideal, which are much shorter than that of other reported materials [33,34]. At such a low operating tempera- ture, the response and the recovery time are short and satisfactory for the applications.