One day in spring 2019, pictures of children started to appear on an online support group for diabetics. Some of the kids were dancing. Some were on the playground. All were proudly showing off a medical device: an insulin pump decorated with a circle, scrawled in green magic marker.
The symbol represented a life-changing development for diabetics and their families — and the culmination of a sprawling, self-directed hacking project. Dozens of people had spent hundreds of hours creating a device that could control a modern, widely-available insulin pump: a do-it-yourself artificial pancreas.