I am not a expert here. But for a software project of mine I was scratching my head for a wearable device which can monitor heart rate continuously (battery efficient). I have one wearable device Sony MIO fuse which measure heart rate using PPG technology which most of the other wearable device use.
I did some research and found some links: https://ieeexplore.ieee.org/document/5504744/ https://www.computer.org/csdl/proceedings/bsn/2010/4065/00/4065a139-abs.html
which is effective and also battery efficient. Also to listen to heart beat the most ancient technique has been through sound only (stethoscope).
Now my question is why wearable device maker are not using this technique. May be using touch microphone we can listen sounds inside body on wrist. Are there any technical complications to it?
Hope my question is not confusing and I am hoping I am posting it to right forum. Please comment if it need improvement. Like I said before this is not a field of my expertise.