Public health guidelines say to avoid crowded indoor spaces during the pandemic. But as schools reopen and people head back to the office, experts are looking for ways to measure how risky it is to share space and air with others. Scientists at Northern Arizona University are trying out an idea: simple carbon dioxide sensors in classrooms and science labs around campus. There’s even one here at KNAU. Science reporter Melissa Sevigny spoke with biologist George Koch to learn more about the project and hear our results.