How do I properly release an open sourced project?

So, I had an idea and started prototyping it.

Keeping things short.... I want to release it as "open source", keeping it available to anyone who wants to make it. (Essentially, keep other companies from getting a patent on the idea).

I'm not a fan of limiting the market, competition leads to growth and I would love to see a few companies run with this idea and see where it goes.

"Prior art" seems to be the way to do this, but what exactly do I need to do? Is posting it online enough? YouTube videos?

Thanks

Edit, just to clarify, this is for a physical product, not software. I only used the term open source because I didn't know how else to describe it.