That's not the case in most states, like California, New York and Massachusetts, due to state laws.
And from what I understood, all inventions they own, but I am still very iffy on what's qualified as an invention.
A coworker even asked for bosses blessing to sell some stuff on the side unrelated to the company, he said no because as per the contract that wouldn't let coworker give full undivided attention to the company.
> Relate at the time of conception or reduction to practice of the invention to the employer’s business, or actual or demonstrably anticipated research or development of the employer
For google, that's pretty much all software related projects.
Given that you work on your own time and don't use company's resources.