Reply to Cue points when I'm not home... PLease help

when i open traktor when my S2 is not connected and try to play a track it will not play thru the speakers on my macbook. It works fine when the S2 is connected to my external speakers so i don't believe its a problem there. But when I'm away from home and want to set up some cue points or beatgrid some tracks its impossible if i can't hear what I'm doing. How can i get it to play thru my macbook when my s2 isn't connected,