I have signed several of these. If you do it on company time or with company resources, it's theirs. If you do it on your own time with your own stuff, it's yours.
You may or may not be shocked to learn how many "personal projects" get done when people are supposed to be doing the work they get paid for or with resources they are effectively stealing from their employer. This isn't some evil corporate attempt to steal your brilliant work. They are trying to make sure that when you are at work using their stuff you are doing your actual job.
If you have your own things you want to pitch as products you will be giving over the rights to that the minute you work on it on company time with company resources.
If your ideas are good, save money, quit, start a start up, and use your connections to make a good deal with them (sell it to them). Or wait until you are a vested shareholder.