SnO/sub 2/ sensors are widely used for the detection of air contaminants such as CO. Nevertheless, their application encounters several problems, mainly the effect of interfering gases. The low selectivity is, in fact, a well-known problem of these sensors. Moreover, the high operating temperature of metal oxide sensors implies, in general, high power consumption. We present a study aimed at the selection of an appropriate measurement technique for detection of CO for indoor applications (lower threshold 100 ppm), in the presence of high concentrations of ethanol (up to 1000 ppm), by using only one sensor. Moreover, the paper aims at developing portable CO detectors that are very small, low power, and could be battery operated.