DB Meter wanted

I work as a guitar tech, roady for a bunch of bands round the globe and I am always working in various sound level situations. I was wondering if anyone has written a simple easy application to turn my macbook into a basic sound level meter, i see they make a few for iPhones and iPod Touch, but i have neither of them.. I have a brand new macbook unibody and always have it side of stage with me as i keep Setlists, Instrument tunings and changes, and my StroboSoft tuner on it. I thought there would be a multitude of simple little downloads for such a thing, but i was wrong. I've spent the past hour seaching the net but come up with nothing..
i basically need a meter and a read out, then i can make changes to my distance from stage, before i finally go deaf..haha
thanks in advance,
Gavin