MQ-3 alcohol gas sensor for measuring fermentation progress?

[Abyssal]

I started looking up how to electronically monitor my fermentation process with a RasPi, and I came across this guy's blog about his Master program thesis where he used an MQ-3 alcohol gas sensor.
https://middlewaresensing.wordpress.com/2010/08/04/wine-monitoring/
I'm just trying to figure out how that would work or if it would be accurate? Because I do like the idea of it mounting to the mouth instead of floating in my vessel for the entire ferment.

 

[Abyssal]

Adding on to this thread, found this thing: https://www.vernier.com/products/sensors/eth-bta/
It's an ethanol sensor, and it looks like it is used mainly for educational purposes. Any one know of any other ethanol sensors or any DIY stuff for it?
I know of the Tilt hydrometer (and the DIY version called the ISpindle) But it seems to me an ethanol sensor would be cheaper hardware wise with about the same amount of coding?

 

[lbispo]

I thought about doing it by monitoring fermenter weight. I'm just concerned about yeast multiplying and not giving accurate results.

The other way would be by measuring the liquid pressure in 2 points at a known vertical distance, as they do on commercial breweries but it'd add a lot of hardware and unfeasible for glass fermenters.