Oura on Thursday unveiled the fifth generation of its popular smart ring, starting at $399. The Ring 5, which Oura describes as the world’s smallest smart ring, arrives just a year and a half after the company launched the Ring 4 and seven months after the Ring 4 Ceramic . The Ring 5 is 40% smaller than its predecessor and comes with more accurate sensing and enhanced battery life. The Ring 5 is launching alongside new software updates that include blood pressure signals, live activity tracking,