Most rule violations don't get noticed. Of those that do, most are ignored. Of those that aren't, most are met with a warning. Most of the time it's sufficient to respond to a warning by: apologizing, pleading ignorance, correcting your "mistake", and promising to do better.
"It's better to seek forgiveness than ask permission."
IANAL.
If any of your side projects get big, depending on the contract your employer might be able to claim ownership of it.
If you're doing side projects despite those kind of contracts, you're effectively trusting your employer to be nice when they have legal right to not be. This isn't a great position to be in.
Your employer is not omniscient. To claim ownership of your side project they first need to know it exists. How will they come to know it exists? Are they even looking for employee side projects?
Your employer is also not omnipotent. It needs to be worth someone's time and energy to come after your side project. Now if it's wildly successful, or competing with your employer's product, or you have internal enemies, that's one thing. But most side projects just aren't worth going after.