This paper presents recent work in measuring carbon dioxide (CO2) using an absorption spectroscopy method within the mid-IR region. A multi-path optical fibre based reflective sensor is proven to be capable of detecting CO2 at lower level (<15%) and higher level of concentration (>15%). For low level detection, the sensor is capable of measuring CO2 concentration from 0.8% to 14.8%, while for high level of detection, the sensor showed its capability to detect CO2 concentration from 15.1% to 44.6% with high accuracy. By eliminating unwanted noises using suitable filtering technique, the voltage response from the system has become more stable and without significant loss in voltage, thus improving the signal-to-noise ratio and stability of the system. The average signal-to-noise ratio for each of the filter types, no filter, lowpass, bandpass were calculated as being 53.4, 69.1 and 119.0 respectively. Similarly, moving average technique was developed in LabVIEW to improve voltage response with less noise and interference, resulting better overall system's performance.