You have a very valid concern. Many IP agreements are overly broad to protect the employer (I know, I write those agreements).

Anything you create while in the scope of employment will be owned by the employer. But, it's debatable whether things you create on your own time or works which you create after employment may be owned by the employer.

What you need to do is seek an IP attorney (one who does business law too) for advice on your specific agreement and plans. The agreement should be negotiable and tailored for you -- if you ask or insist. Please don't go signing something just because 'everyone else does it.'