Not sure if it's quite the same, but Google Fit has a feature that gets your respiratory rate from the selfie camera. They also have one where you put your finger on the camera flash and it uses that to see your bloodflow.

https://www.lifewire.com/measure-respiratory-and-heart-rates...

Very cool, thank you. I'm honestly surprised this dark magic hasn't been (ab)used yet, unless it has some strong limitations.