Don't do it. They can find out anything. As if they were watching a live-stream of what you are doing. By law, employers have access to monitor anything and everything that happens on company property. Company property, in the modern sense, includes laptops, company-issues phones, tablets, and the wired and wireless networks. They have every right to in-near-real-time perform surveillance of what you are doing.
As for employee IP agreements and contracts, it really only becomes litigious if there are large sums of money involved.
There are cases of litigation against 'small fish' I can't find references for at the moment.
In most cases, they will go after you with non-compete (which is not really legally enforceable in California). Technically, if the company you work for is big enough - you can be 'competing' with them.
I know a guy who got into trouble write a <insert favorite programming language> module and putting it in a public repository. The module solved the current task. It was easy to install and had documentation. All good? No. The company claimed he spent extra (meaning unnecessary time) cleaning up the code and making is usable for other companies. Also I think he didn't attribute the company. They claimed full copyright to the module, co-maintainer status and reimbursement (money back from the outsourcing company, not sure if they could have deducted part of the salary).
To be save I would even suggest to invest in a second laptop so the company can't claim you used company resources at home after work.
Many large tech companies make you sign forms stating that even work done at home on your own time on your own laptop is still their property. Whether this is enforceable or not is another story, but they have more money for lawyers than you will.
We had someone walked out from a company for working on their business during the day. I don't know how it was found out but this employee was pretty useless at delivering on their job so I imagine that didn't help.
Oh hell yes. I worked for a transportation company and used to park the van and spend at least 1-2 hours sitting in the van outside hacking away on public wifi. Got caught all the time.
As for employee IP agreements and contracts, it really only becomes litigious if there are large sums of money involved.
For example, Mayo Clinic v. Peter L Elkin, MD
http://www.gpo.gov/fdsys/granule/USCOURTS-ca8-11-02959/USCOU...
There are cases of litigation against 'small fish' I can't find references for at the moment.
In most cases, they will go after you with non-compete (which is not really legally enforceable in California). Technically, if the company you work for is big enough - you can be 'competing' with them.