CO2 sensor (IMAGE) University of Alberta Caption This paper-based sensor turns orange as it is exposed to carbon dioxide. Image courtesy of Al Meldrum. Credit Al Meldrum. Usage Restrictions with credit to Al Meldrum. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.