A system includes a system housing including an inlet, at least one gas sensor responsive to a first analyte gas other than oxygen within the system housing and in fluid connection with the inlet, and a sensor responsive to oxygen within the system housing and in fluid connection with the inlet. The sensor responsive to oxygen is formed to be chemically separate from the at least one gas sensor responsive to the first analyte gas other than oxygen. The sensor responsive to oxygen is responsive to a change in the concentration of oxygen arising from creation of a driving force in the vicinity of the inlet to provide an indication of a state of a transport path between the inlet of the system and the at least one gas sensor responsive to the first analyte gas other than oxygen.