The vast majority of companies ask for a 'we own everything you breathe' agreement as a prerequisite for employment. The vast majority of employed software engineers don't have the luxury to work on side projects, unless they relinquish the IP to their employer for no additional compenstation, which renders monetization moot.
I worked with someone who was working 2 full time 9-5 jobs simultaneously for a few months before being found out. When the company did realize what was going on, they quietly parted ways with him without any punishment, because they didn't want it to get around that he got away with it for so long. I think if you're not at a big organization with a proper legal department, that's the most likely outcome.
Even got promoted to management in one of the two jobs! They would sometimes have to take calls from both jobs with one earbud in each ear connected to each laptop.
The industry the companies were in are not known for employing the best and brightest programmers... so I can understand being able to output enough to keep everyone happy. But it still boggles my mind that they never slipped up and got caught.
Most countries I worked in, anything done after hours, not using company resources, and not in the competition space of the employer is simply allowed. No company would be able to enforce that.
In fact (I have had that happen) if the contract tries to over reach, in particular regarding IP, then that clause could just be made void in court.
