PASens® technology is based on the well-established photoacoustic sensing technology. Narrow-band light matching the absorption bands of CO₂ molecules is emitted into a predominantly closed measuring cell. CO₂ molecules in the measuring cell absorb a part of the irradiated light, whereas other molecules cannot contribute to absorption due to the spectrum of the emitted light. The more molecules present in the measuring cell, the larger the absorbed energy. The absorbed energy of the CO₂-molecules excites mainly molecular vibrations, which results in an increased translational energy of the molecules and, due to the closed measuring cell, in an increase of pressure in the cell. A modulation of the light source causes a periodic pressure-change in the measuring cell, which can be measured with a microphone. The signal of the microphone thus serves as a measure of the number of CO₂ molecules present in the measuring cell and can be used to calculate the CO₂ concentration.