You need a hydrometer. When the level sits for a week or two, you're done or stalled (if it seems too high). They are liek 5-7 bucks and will allow to you calculate abv, if its still fermenting and other fun stuff.
I made a few batches without one, but airlock activity isn't an indicator of finished fermentation. It just shows a bell curve unique to that current batch of if its started to fire up or wind down. If you can't go buy one (you definitely should), I've waited as long as three months to rack once, so you're probably fine waiting a long period of time to rack. But seriously, go get yourself a hydrometer.