Half empty or half full?
Telling if bottles are full or nearly empty

Just a quick idea. With food, we can tell if it has been untouched or eaten, or what have you, but we don't have this for big bottles of alcohol. Wine bottles, vodka, et cetera. Would it be possible to add something where we could tell if a bottle has been opened, is two thirds full, half full, or nearly empty? That sort of thing. It can be kind of confusing when you have lots of booze for an event, but can't tell if all the bottles only have one serving in them.

Thanks!

*burp*