If you’re an employee (not contractor) in California, your employer can specify in the employment contract that they own IP rights to anything you make even in

If you’re an employee (not contractor) in California, your employer can specify in the employment contract that they own IP rights to anything you make even in your own time, as long as it “relate[s] [..] to the employer’s business, or actual or demonstrably anticipated research or development of the employer”. Many tech companies do so, including large tech companies whose business relates to just about everything. YMMV if you’re in another jurisdiction.