Professional inventors will tell you that good ideas alone are a dime a dozen, you probably have to put some skin in the game in the form of time and money to produce some product prototype to advance the idea.

Aside from the expensive patent process, or paying some inventor assistance service thousands to develop and promote it, there is the Crowd Inception Service Quirky.com where you can earn royalties for a product should it be developed.

You could learn some and search for an existing patent similar to your idea at the patent office:

http://patft.uspto.gov/

What if you discovered how easy it is to sell ideas online if you have the right business plan for top notch marketers? Here are 3 simple steps to get you started...

the latter - generally you have a full year before whatever unique idea you have has to either be trademarked (the former) or becomes public domain, so you can do both if you do the latter.

Ok, so I came up with an idea and it adds a very useful feature to cars that would assist the driver. However, I'm not sure how to go about selling the idea to car companies. Should I patent the idea and then try to get the company to buy the patent, or should I try to start a company that sells that specific product to car companies?