Send out applications. If you get a call back obviously step outside and talk with the recruiter. Schedule all of your phone interviews near lunch time so when you are out getting lunch, no one notices. When you do have the in person interview call in sick the morning of - or say you have a Drs appt at the time of the interview.

The biggest thing here is you don't want to get caught applying places because in the event you can't find a job, your current employer will likely write you off w/ regards to future promotions.

One thing so also think about is how close are you to your boss? If you guys are really tight, I would give them a heads up. I would only give them a heads up once you get a serious offer. If it's just some person you don't really care for I'd follow the strategy above.

This experience/information may be overkill for your current position, but as you grow your career it will be more beneficial.