Oura, a Finnish startup that creates a smart activity- and sleep-tracking ring, has raised $28 million in a series B round of funding from Google's Gradient Ventures, Jack Dorsey's Square, and Forerunner Ventures. Founded out of Oulu, Finland, in 2013 Oura monitors the user's pulse, movement, and temperature to deliver a "holistic picture" of their health. And unlike many other health-trackers on the market, the Oura is not worn on a person's wrist -- it slides firmly onto their finger instead. The titanium ring features infrared LEDs, NTC temperature sensors, an accelerometer, and a gyroscope, and can last up to one week on a single charge. Each day, the user can view their data inside the Oura mobile app, with three scores allocated based on their sleep and activity.