Energy beams with different wavelengths or wavelength ranges may be passed through a gas sample in a test chamber. Ones of the energy beams may have wavelengths or wavelength ranges that are absorbed by particular gases. To determine whether any of those particular gases are in the gas sample, the loss of energy, if any, as the beams pass through the gas ample may be determined. The presence of one or more gases that do not absorb the energy beams may be determined by placing a chemical reactant that reacts with those one or more gases and then detecting a chemical reaction between the chemical reactant and the gas sample.