Apple’s recently released Series 6 smart watch incorporates a new medical feature: it can measure your blood oxygen levels. The tech must have been years in the making, but the timing of its release worked well given we are in the middle of a global respiratory pandemic.

The amount of oxygen in the blood is important medical information, and in hospitals is usually measured with a device called a pulse oximeter, which shines a light through the finger or earlobe. Blood carrying more oxygen absorbs …