All tech company jobs I’ve had (in California) had IP assignment clauses. They are not illegal. CA companies can claim ownership of IP produced by employees on their own time and equipment if it “Relate[s] 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”

This is a huge loophole for larger companies who can argue that everything you do may relate to their future business.

1: https://news.ycombinator.com/item?id=21754139