https://www.theguardian.com/technology/2024/oct/15/oura-ring-4-review-best-smart-ring-battery-upgrade > Sleek, celeb-favoured gadget tracks sleep, activity and heart health without a smartwatch, but comes at high cost > Oura’s stylish smart ring worn by celebrities and athletes alike has slimmed down for its fourth iteration, making it easier to put on, more comfortable to wear and last longer between charges.