ALLNET 4duino Pulse Heart Rate Sensor Module Product Model: OKY3471 XD-58C Pulse Rate Sensor Heartbeat Heart Rate Detector Module for Arduino Product Description
This XD-58C pulse sensor module is used to measure heart rates. It's widely applied for developing heart rate related interactive works.
It also has an open source APP program that can display your heart rate real-time in graph. It's in short, a heart rate sensor integrated with optical amplifier and noise elimination circuit.