During the second year of my preparatory class, I had to present for competitions a TIPE. That means a project I had realised during 10 months on a personal subject. Mine was about measuring a CO2 level in a classroom to then conclude thanks to math about the probability of airborne transmission of COVID-19 for the students. To do it properly, I have built a system with a rudimentary gas sensor (MQ-135 on the picture) and Arduino language. Yet, my sensor wasn't very functional so I met an IT and mechanical engineer named Sebastien who helped and gave me a new and really better gas sensor (SCD-30 sensirion). As a consequence, I managed to achieve my project.