FibriCheck measures your heart rhythm by registering the color variation of the blood in your finger. This technique is called photoplethysmography (PPG) and uses the camera and the flash of the smartphone.
With every heartbeat, blood is pumped through the body, which will result in a blood pressure wave that spreads through the body. When this blood pressure wave arrives at the fingertips, the blood vessels expand and the amount of blood in these vessels will increase. Heart rate and heart rhythm can be analyzed by measuring the changes in light absorption as a function of time.