We are getting quite a few queries - FIRSTers are an inventive bunch! And we've repeated this advice often enough to post it ...
Young inventors often toil away on a great idea only to see it already exists. Before you put too much time into your invention do serious research and figure out if it is unique. Your idea can't pre-exist in any "prior art" (invalid, valid or abandoned patent applications, scholarly publications, trade journals etc) or in combinations of "prior art". If the invention seems unique, does it have commercial value?
I refer you to
http://www.ipwatchdog.com/ to get ideas for patentability searches. My son is of counsel to the firm that supports this web site. There is a lot of great information for inventors!
HTH