The text and keywords you have chosen will be shown immediately on a zero results search page on your site. Try it out:

Finally, if you use our Google Analytics connector, we are tagging the zero results page with /no_results_search.html so that you can easily see in Google Analytics how many times these zero results pages occur.

You can now see which search terms resulted in a zero results page! Are visitors looking for something they expect you to have? Or perhaps a small update to your caption will make sure that visitors will find something relevant the next time...