In California, Labor Code 2870 allows you to keep inventions conceived or reduced to practice entirely on your own time and without use of an employer's resourc

In California, Labor Code 2870 allows you to keep inventions conceived or reduced to practice entirely on your own time and without use of an employer's resources unless such inventions "relate at the time of conception or reduction to practice . . . to the employer's business" or to "actual or demonstrably anticipated research or development of the employer." "Relate," in this sense, can be read pretty broadly and so there is always theoretical concern over this issue if you as an employee developed something on the side. In practice, though, there is quite a broad scope for employees to do side projects without having them swept in by such clauses. The exception is where you use expertise that is directly related to your job duties to come up with a better way of doing things in the very area in which your employer competes. Common sense suggests why that should be an exception: if the rule were otherwise, any employee could basically claim job-related inventions as his own. If you have already left employment, and have not yet developed anything, then you should normally have little risk of having your ideas being deemed to belong to your employer. It is normally virtually impossible for an employer, for example, to prove that you were still employed "at the time of conception or reduction to practice" of your idea, as opposed to afterward. Two important exceptions to watch out for on this point: (1) if you file a patent application shortly after leaving employment relating to your employer's field, this is like waving a red flag in your employer's face that you had conceived the invention while employed; and (2) some assignment-of-invention agreements set forth a rebuttable presumption that any invention you develop within x period of leaving employment is presumed to have been conceived while still employed, and the legal effect of this sort of clause is to treat such an invention as belonging to your employer unless you can affirmatively prove otherwise (an often impossible task).