Christina Farr, CNBC:

Tim Cook has been spotted at the Apple campus test-driving a device that tracks blood sugar, which was connected to his Apple Watch.

A source said that Cook was wearing a prototype glucose-tracker on the Apple Watch, which points to future applications that would make the device a “must have” for millions of people with diabetes — or at risk for the disease.

If Apple can crack this problem, a bloodless, continuous, glucose tracking Apple Watch, they’d help a lot of people, sell a ton of Apple Watches at the same time.