The older I get, the smaller my cubicle gets. In fact, I don't even have a cubicle now. But my boss used to walk in undetected and catch me doing research for some assignment (WWW - to the boss it looked like web surfing) and he would tell me to get to work. I wanted to put a cowbell around him, but I'm sure he wouldn't go for it, so I had to come up with something else. (note - the title should be "Flatulent.")
Step 1: Picked up this nifty noise maker for about 6 bucks in the toy section of the food store.
You can read the package for yourself. It has about 6 different random "tunes." But, the key item is the little RF remote button that comes with it.