Is there case law on this? The CA moonlighting law heavily implies that a huge company could claim to own nearly anything you produce (as an exception that proves the rule).
> (a) Any provision in an employment agreement which provides that an employee shall assign, or offer to assign, any of his or her rights in an invention to his or her employer shall not apply to an invention that the employee developed entirely on his or her own time without using the employer s equipment, supplies, facilities, or trade secret information except for those inventions that either:
> (1) 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; or
> (2) Result from any work performed by the employee for the employer.
A huge company like Google can claim nearly anything relates to their business, so they could trigger (1) even if you don't do that kind of work for them.
In practice, I agree they usually don't care about side projects and wouldn't take action even if you didn't get an exception, but there is substantial risk if you are contributing to a significant project that ever attracts their gaze.