Scientists have long been interested in creating portable devices that can quickly and painlessly screen a person for disease simply by taking a whiff of their breath. But delivering on this dream has proved to be a challenge. Different diseases may cause similar breath changes. Diet can affect the chemicals someone exhales, as can smoking and alcohol consumption, potentially complicating disease detection. Still, scientists say, advances in sensor technology and machine learning, combined with new research and investment spurred by the pandemic, mean that the moment for disease-detecting breathalyzers may have finally arrived. “I’ve been working in the area of breath research for almost 20 years now,” said Cristina Davis, an engineer at the University of California, Davis. “And during that time, we’ve seen it progress from a nascent stage to really being something that I think is close to being deployed.”