It's pretty obvious that your employer owns work you do for your employer, and things you do on company time or using company equipment. But this "they own everything you do forever even at 2AM at home using your own computer" meme gets repeated all the time and it's complete bullshit regardless of what's actually in your employment contract. And this ignores the fact that the vast majority of employees in the US don't have employment contracts at all and/or live in states that explicitly make these broad types of IP assignment clauses illegal or at least unenforceable.