The MAX30102 is a very versatile sensor and it can also measure body temperature other than heart rate and blood oxygen level. This is a sensor designed by Analog Devices and features two LEDs (one Infrared and one Red), a photodetector, optics, and low-noise signal processing unit to detect pulse oximetry (SpO2) and heart rate (HR) signals.
The main idea is that you shine a single LED at a time and check the amount of light that is getting reflected back to the sensor. Based on the reflection you can determine the blood oxygen level and heart rate.
We can interface MAX30102 sensor with any microcontroller or development board to get the SpO2 or heart rate values. Here is the complete tutorial which covers how to interface MAX30102 sensor with Arduino.
