[nradov]

Heart rate will probably be tough without a dedicated sensor. Sennheiser now sells earbuds with an optical HR sensor but accuracy is bad.

https://www.dcrainmaker.com/2024/05/sennheiser-momentum-temp...

Respiration rate is harder. It requires precise heart rate variability data to detect the start of a breath.

[pedalpete]

I wonder if "accurate enough" hr could be achieved through filtering accelerometer data? You'd have to be quite still, but if the device knows you're doing push-ups, and what range your heart-rate could be in, it may be able to filter out other movements.

Respiration can be measured with microphones, and again, movement, but I suspect this may be more challenging than filtering HR.