IF the contract you signed still gives your former employer rights over intellectual property (IP) you develop post-employment,, then--subject to the precise terms of that agreement--the former employer would own your IP, because in that case, you contracted away your rights. But if the contract only applied to IP developed while employed, the former employer would only have rights to it if it could be shown that you in fact developed it (or significant parts of it) while employed or through the use of company resources and materials.