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.

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.