Don't you hate it when someone bursts into your conference room during a meeting without knocking? Stop taping "room in use" signs on the door and install the Brighthandle: part door handle and part gatekeeper.

The Brighthandle, developed by a company based in Stockholm, normally glows green when a room is empty. When you enter the room however, just flip the thumb turn of the door handle to toggle the light to red so people know the room's occupied. A handle on the inside glows the same color as its outside sibling, reminding you that you are, in fact, in your own conference room. And if you have trouble remembering where you are outside of the room, we have some other gadgets to recommend.
— Nino Marchetti

Brighthandle, via Techie Diva