In this study, gas sensing properties of ferrocene functionalized multi-wall carbon nanotubes (MWCNT) and iron oxide nanoparticles were investigated via acoustic wave and electrical based techniques. Commercially obtained multi-wall carbon nanotubes having amine functional groups grafted directly onto their surfaces were covalently functionalized with ferrocene molecules. Iron oxide nanoparticles synthesized by the alkaline coprecipitation of ferric and ferrous salts were functionalized with ferrocene molecules. Dispersions of each modified nanoparticle in 3 mL ethanol were prepared and sonicated for 12 h in order to ensure adequate homogeneity. 5 L from each of these dispersions were then drop-cast onto AT-cut gold coated quartz crystal microbalance (QCM) and gold interdigitated (IDE) glass electrodes with 3 m interdigit spacing followed by drying on hotplate at 60 °C for 30 min to deposit thin-films. The thin-film coated electrodes were exposed to alternately varying concentration levels of CO, CO2, O2 and humidity ranging from 0 vol% to 100 vol% in predetermined intervals by a computer controlled mass flow meter array in an electromagnetically shielded and hermetically sealed measurement cell specifically designed to acquire QCM and electrical signals from the electrodes. Gas sensor responses of the thin-film coated QCM electrodes were assessed by measuring the frequency shift of the vibrating quartz crystal from its natural resonance frequency and evaluating that value into adsorbed mass according to Sauerbrey relation, whereas, responses from the interdigitated electrodes were assessed by measuring the resistance changes through the thin-film coating under a compliance current value of 1.0000 mA.