An appliance is disclosed for measuring at least one gas analyte in exhaled air. In at least one embodiment, the appliance includes an inlet opening for the introduction of exhaled air (mouthpiece), at least one measuring chamber for receiving a sensor unit, and a conduit which provides a fluid connection from the opening to the measuring chamber, and wherein, depending on the gas analyte that is to be measured, a sensor unit with a suitable gas sensor can be introduced into the receiver.