Photoplethsymographic heart rate requires a lot of algorithmic compensation for noise and motion artifact. There are some pretty sophisticated strategies availa

Photoplethsymographic heart rate requires a lot of algorithmic compensation for noise and motion artifact. There are some pretty sophisticated strategies available for beat interpolation, but individual R-R intervals are tremendously more difficult to recover accurately against real-world noise. HRV measurements are also very intolerant to error in R-R interval, and even less so to dropped beats. There are certainly conceivable solutions to these problems, but no major manufacturer of PPG based consumer heart rate devices allows access at a level low enough to get R-R time series or understand R-R interval confidence. OEM module manufacturers for pulse ox devices do allow direct serial access to the PPG waveform for those interested in hacking at it.