A micromachined integrated opto-fluidic or opto-acoustic sensor having a rapidly intensity-varying or pulsing light source, an interference filter, a gas cavity, which may or may not be an optical and/or acoustic resonator tuned to a particular wavelength of light, or sound frequency, into which the detected gas can diffuse into via a filter, and a fluidic or pressure sensor to detect the heating and cooling, and the resulting expansion and contraction of the gas due to the absorption of light at the particular wavelength by the specific gas being detected. The presence of other gases is inferred from the detected gas.