The SparkFun Photodetector Breakout includes the MAX30101, a highly sensitive optical sensor and successor to the MAX30105 and MAX30102. The MAX30101 Breakout utilizes a photon detector to measure the amount of returning light that is reflected back from the LEDs. This is useful for various applications like particle (i.e. smoke) detection, proximity measurements, and even photoplethysmography.
The MAX30101 utilizes a red LED, a green LED, and an IR (Infrared) LED for presence sensing, heart-beat plotting and heart-rate monitoring among its multitude of uses, including Pulse Oximetry. Sparkfun has written an Arduino library and Python package for the MAX3010x which takes care of all of the I2C communication, bit shifting, register writing and sample reading.
More information is available on the website of Sparkfun.