Different thermometers have been constructed over the decades to measure the temperature of the body to help detect and monitor morbid states. They yield slightly different estimates of the core body temperature depending on the proximity of the measurement site to the internal milieu of the organism, the principle of temperature assessment, and the specific characteristics of the gauging devices. Evaluation of the exhaled breath temperature (EBT) has been recently suggested as a new method to detect inflammatory processes in the conducting airways due to changes in the blood flow perfusion of their walls and adjacent structures. While the first reported EBT experiments required sealed laboratory environment and sophisticated equipment, we designed a simple handheld instrument for EBT measurement and proven its precision, reproducibility and validity in subjects with asthma. We now describe the construction principles of our instrument, the procedure to test the fitness for purpose of the separate units and the novel features of the newest prototypes outfitted with microprocessor and memory. We also outline the potential clinical applications of an individual device for EBT measurement.