how do watches measure blood pressure
It includes a sensor strapped to the wrist which can measure the pressure in the aorta, the main artery close to the heart, where high blood pressure does most damage. A sensor in the watch records the pulse wave of the artery, which is then fed into a computer together with a traditional blood pressure reading from a cuff. In most people the pressure in the aorta is 10mm Hg lower than in the arm, but in some, especially younger people, it is as much as 30mm Hg lower.