As John Keefe notes in his project writeup, at-home pulse oximeters — which monitor the oxygen saturation in your blood — have been selling out due to the COVID-19 pandemic. While you could try hunt around and find one, he decided to instead make his own device using a SparkFun Pulse Oximeter and Heart Rate Sensor module and an Arduino Uno.

The sensor takes pulse and oxygen level readings from your fingertip, then shows the resulting numbers on an RGB NeoPixel shield. Although the unit is not medically approved to diagnose or treat medical conditions, it’s a neat display method, and it even features heart and lung icons to indicate what you’re seeing. 

Code for the build is available on GitHub.