This is a very touchy area. You have to get buy-in from your employer for side projects, otherwise they (with some legal standing) believe they own the work.

This is a very touchy area. You have to get buy-in from your employer for side projects, otherwise they (with some legal standing) believe they own the work. The only alternative is to be very discreet about what you do on the side. It's wrong, but see how companies react...