I didn't know a better place to ask this, so here it goes. For activity trackers, Fitbit has the Charge HR with an optical heart rate monitor, while Jawbone has the UP3 with a bioimpedance sensor for heart rate. 

Can you please explain the differences between the two. Also, diagrams would make it more understandable. 

Info about optical sensor:
[electronicdesign.com/displays/build-your-own-optical-heart-rate-sensor](http://electronicdesign.com/displays/build-your-own-optical-heart-rate-sensor)
Also, are any diagrams [from here](http://electronicdesign.com/digital-ics/build-wrist-heart-rate-monitor-using-ultra-low-power-mcu) relevant?

On Jawbone's blog, there is some info:

> 
> Bioimpedance measures the resistance of body tissue to tiny electric
>  current to enable the capture of a wide range of physiological signals
>  including your heart rate. If you've ever measured your body
>  composition such as fat content, this is very similar. Our choice to
>  use bioimpedance technology sets us apart in three key ways:
> 
> 
> Battery life. Because bioimpedance requires significantly less power
>  compared to optical sensors for same level of accuracy, we can deliver
>  a smaller form factor and longer battery life Physiological signals. A
>  single platform utilizing bioimpedance sensors captures a wide range
>  of signals: heart rate, respiration rate and galvanic skin response
>  (commonly known as skin conductance) Updatable technology. Given the
>  versatility of the sensor platform, we are able to (and we will)
>  unlock exciting new features with a simple, free, over-the-air
>  firmware updates in the coming months
> 
> 
>