Emma Black was diagnosed with Type 1 diabetes in late 2014. Because diabetics' bodies don't produce insulin, they need to be constantly aware of a lot of different numbers: their carbohydrate intake, their sugar levels, how much insulin they need to inject to break that sugar down.

High sugar levels over time can cause complications like heart disease, kidney failure, blindness, or circulatory problems that result in amputation; in the short term, sugar levels that are extremely high or low can put a person into a diabetic coma, which could be fatal if it's not properly treated.

Black couldn't believe how inconvenient it was to check her glucose levels—it involves carrying around a bulky device and plugging it in to a computer to see the data elsewhere, Black, then known as Stephen, writes in a blog post from early 2015. "If a loved one wanted to check in to see if I was doing all right, they would need to call me and hope I answered," she wrote.