Hey all, I did a quick search and didn't see this anywhere, but if it is then I apologize for the repost. This is an easy trick to track your brew's carbonation...
All you need is an empty water bottle.
When you are bottling your brew, siphon some into the empty water bottle until it is about half full or less. Then take the bottle, squeeze out all the air until the liquid reaches the lid. Then close the cap and your bottle should stay "crushed up" for lack of a better term. (bottle on the left in the picture)
Once your beverage begins to carbonate, the air will begin to fill up the bottle and push out the sides. Depending on how much liquid you put you, your bottle will expand until it seems like it will almost explode! I've never had this happen but if you're worried just open the cap and let out the air and you'll know its close or ready. (BTW finished carbonation is bottle on right in picture)
This way you don't have to open any full bottles in anticipation! For all of those who say you're still wasting some good beer, I do drink my tester but I'm guessing its not good for you haha. Alright, well enjoy and let me know if you have any other tricks of the trade!