I don't think consumers would accept this but for athletes there has been some research that the EARLOBE might be the ultimate single point for measurement

They can even measure blood pressure in lab tests during MOVEMENT at the earlobe

Heartrate, spO2, temperature and it's even a good location for very low level of sound to be heard

Again consumers would never adopt an earlobe cuff, well maybe it was artistic somehow and not heavy/distracting

But athletes would use whatever works

If I had millions I'd invest in development, so steal this idea?