I'm sure that this has been mentioned hundreds of times on here and other web sites but I'll say it again... an air lock that isn't visibly bubbling isn't an indication that fermentation is over.
Let's take that sentence apart and look at some of the reasons why:
- Fermentation may have slowed and you're not seeing a bubble during the time you're watching.
- Stuck fermentation.
- CO2 is escaping through another route (like around the bucket lid)
- All three of these.
So, aside from not seeing active bubbling, how can you tell when fermentation is over? The generally accepted way is for your gravity reading to be the same for 3 days in a row (you would normally see this at or very near your predicted FG).
OK, so what do you do if you don't have a way to measure gravity? Let the fermenter sit there for a MINIMUM of 10 days. It won't spoil or go bad as long as the two enemies of beer (light and oxygen) aren't introduced. C02 is heavier than Oxygen, so part of the natural process is that Oxygen won't be introduced (don't slosh it around) and as long as you're fermenting in a dark room, light shouldn't be an issue (opening the door and looking won't hurt it).