The £500 'smart ring' hailed as England's Euros 'secret weapon': High tech Oura band loved by Prince Harry and Kim Kardashian claims to boost performance with 24/7 monitoring of  your sleep, heart rate and breathing

It's not every day that a brand can get Prince Harry and Kim K to wear a piece of its jewellery. However, Finnish brand Oura has successfully enticed them into wearing its titanium ring.