Most people don't have side projects. Most companies have zero interest in taking ownership of your unrelated hobby project.
The exception is if your side project overlaps with your employer's core business. Example: If your employer makes database software and your side project is an iPhone game for kids, they have zero interest in your IP. It would be a waste of their time and money to seize it, and they aren't going to allocate resources to running it.
On the other hand, if you're employed develop database software and you also create a database side project while employed there, then yes, your employer will have valid claim to that IP.
The closer your side project is to your day job, the more interested they'll be in taking it. You can't collect a paycheck from a company, have access to their IP, while simultaneously working on a competing project in secret.