Startup launched on crowdfunding platform in 2015 has since sold 5.5m rings worldwide and is valued at $11bn Stylish Finnish-American smart ring company Oura may be the darling of wearables, adorning the fingers of celebrities and sportspeople, but it is not resting on its laurels as it heads towards an IPO later this year. This week it launched the world’s smallest smart ring, the Ring 5, its latest evolution of the device that defined a whole category. The Ring 5 is 40% smaller and with longer