Photoplethysmograph sensors simultaneously measure vital signs and changes in the amount of blood hemoglobin and electrocardiograph sensors measure minute voltage fluctuations from pulse. When mounted on a mobile phone these sensors make it possible to monitor pulse and oxygen saturation level while exercising. If mounted on a game controller, they can display player excitement and stress levels to increase the thrill of game playing by allowing players to read each other's emotional states. (a related article)