I'm just saying you could probably find one of those devices. It sounded great in theory, but actually doing it, well, it's just plain awkward to come to someone's cubicle and there's a yellow light. It's not red, but it's not green. What do you do next?

For extra fun times, the owner of the company tended to just ignore everyone else's red and yellow lights, and he kept working in an office with a door that he closed.