The rapidly expanding severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its variants demand a continuous monitoring method through portable and wearable devices. Utilizing the rich surface chemistry and high chemical-to-electrical signal conversion of 2D MXene-graphene heterostructure thin films, a field-effect-transistor (FET) sensor, which has a flexible substrate to be assembled onto the mask and combines with a Bluetooth system for wireless transmission is developed, to detect the influenza and SARS-CoV-2 viruses in air and breath. At first, the developed sensors are examined in the laboratory through direct contact with sensing targets in solution form. The results show a low limit of detection (LOD) of 1 fg mL−1 for recombinant SARS-CoV-2 spike protein and 125 copies mL−1 for inactivated influenza A (H1N1) virus with high specificity in differing recombinant SARS-CoV-2 spike protein and inactivated H1N1 virus. Then the sensors are tested under various simulated human breathing modes through controlled exposure to atomizer-generated aerosols in an enclosed chamber and mask coverage. The results show the high sensitivity of the developed sensors under varying distances to the source, viral load, flow rate, and enclosed conditions. At last, clinical tests are carried out to demonstrate the robustness and potential field applications of the sensors.