A fully autonomous and fast chemical gas sensor system is presented. This proof-of-concept device is based on the exploitation of the dissipated power at individual nanowires by Joule effect induced by the bias current applied in conductometric measurements (self-heating), which enables heating the tiny mass of these wires up to the optimum temperature for gas sensing applications with power values as low as a few tens of μW. Here, this interesting feature is exploited to develop a sensor system that only requires few mW to bias, heat and measure the response of the sensing material. This power value can be supplied by state-of-the-art energy harvesting technologies, such as thermoelectric microgenerators. We also demonstrate that using a single nanowire reduces the thermal inertia of the sensors, minimizes gas diffusion processes, and results in fast dynamic responses only limited by the surface reaction kinetics. For all these reasons, the here-presented system is an important step forward towards fully autonomous and distributed gas sensor networks based on ultra-fast devices without the need of battery replacement.