Dean Gouramanis is building a wearable Bluetooth-enabled Arduino Pulse Oximeter:

Comprehensive Respiratory Health Monitor

bluetooth-enabled wearable device can measure Pulse Oximetry, and ambient CO2 24/7

https://hackaday.io/project/7798-crhm-comprehensive-respiratory-health-monitor

https://hackaday.io/project/7798-crhm-comprehensive-respiratory-health-monitor

https://hackaday.io/project/7798-crhm-comprehensive-respiratory-health-monitor

https://hackaday.io/project/7798-crhm-comprehensive-respiratory-health-monitor

The board is shared on GitHub:

 dgouramanis/CRHM