Your LBS has a chain wear measuring tool. It's cheap and I recommend getting one. I think they are about $15.00. I check my chain wear often and as soon as it gets close, I get a new chain.
There is no need for a special tool to do that. A simple ruler will do the trick, every other pin should be 1 inch apart. Here is a link to better describe the chain measuring process.
http://sheldonbrown.com/chains.html