# Basic Box2D collision detection

I don't understand how to listen for collisions in Cocos2D/Box2D. Say I have two dynamic circle bodies. One is very small and the other is relatively large. When the small circle collides w/ the large circle I'd like to do something (play a sound for example). What's the best way to do this?

I'm currently experimenting w/ the TestPoint method. Something like:

if(largeCircleBody->GetFixtureList()->TestPoint(smallCirclePoint)){
// collision happened...
// play sound etc
}