DFRobot Gravity Expansion Shield and Sensors for Arduino - DFRobot SEN0203, The DFRobot heart rate sensor is a thumb-sized heart rate monitor designed for Arduino micro-controllers. This heart rate monitor sensor is a pulse sensor which is developed based on PPG techniques. This is a simple and low-cost optical technique that can be used to detect blood volume changing in the micro-vascular bed of tissues. It is relatively easy to detect the pulse component of the cardiac cycle according to this theory.The sensor has two holes that you can use to attach to the belt. You can wrap it on your finger, wrist, earlobe or other areas where it has contact with your skin.The sensor has a Gravity interface allowing plug & play connection. The DFRobot IO sensor shield is the best option to connect this heart rate sensor to your Arduino or other micro-controllers. The sensor can also be used with Raspberry Pi, Intel Edison, Joule and Curie by virtue of its 3.3V input voltage. DFRobot SEN0203 Grav