We report on local CuO nanowire growth on microhotplates combined with in situ measurement of the electrical resistance for well-controlled integration into conductometric gas sensing devices. Discrete current steps were observed during the CuO nanowire synthesis process, which is attributed to individual nanowire connections being formed. The high gas sensitivity of the CuO nanowire devices was confirmed by detection of carbon monoxide CO in the low-ppm-level concentration range. Furthermore, we demonstrate that CuO nanowire growth inside a gas measurement setup allows studies on gas sensor poisoning/deactivation processes. A significant decrease of CO response was found after controlled exposure to humidity, which suggests sensor deactivation by surface hydroxylation. Thus, our approach could be a novel and simple way for revealing new insights in various gas sensor degradation mechanisms in the future and might also be adapted for different metal oxide nanomaterials.