There are three billion smartphones bouncing inside pockets and bags around the world. Their owners are often within arm’s reach 24-7. With such ubiquity, constant usage, and connectivity, researchers have publicly drooled over the potential for mobile devices to become gushing conduits of health information. They could wirelessly and effortlessly provide data on patients’ symptoms, the success or failure of new treatments, and the progression of diseases—streamlining clinical trials, research, and personalized care.

The potential is there. But reality is not, according to a study published this week in Nature Biotechnology.