Sensors to detect inside liquids temperature and percentage of alcohol
You actually measure the specifc gravity of the wort, not alcohol. A hydrometer (or refractometer) is used.

As sugar converts to alcohol, SG falls. this is predictive. Alcohol is set by sugar content not temperature. Temperature just affects speed of the fermenation (and taste), not the final alcohol.

An interesting alternative would be measure the CO2 outgassing. e.g. count bubbles through the airlock.
If you look at those graphs you see that 20l of wort will loose 2kg of CO2, so weighing it can also work.

If you want relative fermentation action, then counting bubbles through the airlock U would be the way to go. You could use capacitive sensing, optical or just fine stainless wires through the U of a plastic airlock.

If you use a hydrometer start and finish and calculate the alcohol, then you could later calibrate each bubble to alcohol.