Now I would like to take credit for this idea but I can't. But I never said I'd give credit where credit is due so..
Here's what you do: Buy a fake security camera thing like the one below. Set it up facing someone in your office that you'd like to prank. Then add an official-looking Do Not Tamper sticker below the camera and watch as your prankee behave like he's the most well-behaved employee this side of The Office.
Seriously though, credit goes to mauxly.