A gas sensor (400A-400N) for detecting target gas and test gas, comprising: a housing defining an opening to an external environment; a sensing electrode disposed in the housing and configured to generate a test gas signal when the sensing electrode is in contact with a test gas; a membrane disposed in the housing between the sensing electrode and the opening in the housing, wherein the membrane is at least partially exposed to the external environment; a test gas diffusion path defined in the housing for the test gas to travel in the gas sensor (400A-400N) and comprising an inlet and an outlet; and a capillary disposed between the sensing electrode and the outlet of the test gas diffusion path, wherein the test gas diffusion path is disposed between the membrane and the capillary, the test gas diffusion path including a first wall and a second wall that define the test gas diffusion path, the first wall defining a first test gas diffusion path opening to expose the test gas to the membrane, the second wall defining a second test gas diffusion path opening to expose the test gas to the capillary and sensing electrode, the first test gas diffusion path opening disposed prior to the second test gas diffusion path opening along the test gas diffusion path in a direction of flow from the inlet of the test gas diffusion path to the outlet of the test gas diffusion path, such that when the test gas travels through the test gas diffusion path from the inlet to the outlet, the test gas comes in contact with the membrane prior to coming in contact with the capillary and then the sensing electrode, wherein a total amount of the test gas signal is higher when the membrane has a high degree of restriction of gas access compared to the total amount of the test gas signal when the membrane has a low degree of restriction of gas access, and wherein a magnitude of the test gas signal indicates a degree of restriction of gas access by the capillary. a housing defining an opening to an external environment; a sensing electrode disposed in the housing and configured to generate a test gas signal when the sensing electrode is in contact with a test gas; a membrane disposed in the housing between the sensing electrode and the opening in the housing, wherein the membrane is at least partially exposed to the external environment; a test gas diffusion path defined in the housing for the test gas to travel in the gas sensor (400A-400N) and comprising an inlet and an outlet; and a capillary disposed between the sensing electrode and the outlet of the test gas diffusion path, wherein the test gas diffusion path is disposed between the membrane and the capillary, the test gas diffusion path including a first wall and a second wall that define the test gas diffusion path, the first wall defining a first test gas diffusion path opening to expose the test gas to the membrane, the second wall defining a second test gas diffusion path opening to expose the test gas to the capillary and sensing electrode, the first test gas diffusion path opening disposed prior to the second test gas diffusion path opening along the test gas diffusion path in a direction of flow from the inlet of the test gas diffusion path to the outlet of the test gas diffusion path, such that when the test gas travels through the test gas diffusion path from the inlet to the outlet, the test gas comes in contact with the membrane prior to coming in contact with the capillary and then the sensing electrode, wherein a total amount of the test gas signal is higher when the membrane has a high degree of restriction of gas access compared to the total amount of the test gas signal when the membrane has a low degree of restriction of gas access, and wherein a magnitude of the test gas signal indicates a degree of restriction of gas access by the capillary.