By the time they reach school age, about 90 percent of children will have experienced a condition in which fluid fills the middle ear, muffling sound and sometimes triggering infection. Diagnosis usually requires a visit to a specialist—but researchers have now developed an app that detects this fluid just as accurately, with only a smartphone and a paper funnel.

“Based on the size of the problem, we really wanted to design a technology that could detect it accurately, and also be accessible to a wide audience,” says Justin Chan, a doctoral student at the Paul G. Allen School for Computer Science & Engineering at the University of Washington. Chan is lead author on a new study that tested the app, published this week in Science Translational Medicine.