A method, and a related device, for obtaining the blood pressure of a person. The method comprising steps of providing a light source (101), and an optical sensor (103) configured to detect light from the light source which has propagated through the wrist of a wearer of the device. The amount of light propagating through the wrist depends on the amount of blood in the wrist. Blood pressure is then observed by monitoring the difference in the amplitude of blood pulsation within the wrist when the wrist is lifted above heart level, and when the wrist is lowered below heart level.
