After a number of frustrating episodes for my wife and I, we came up with a plan. At my home office desk, I've got a 5x7 index card with a big red dot on one side and a big green dot on the other, which I use to communicate whether I'm interruptible. When green is showing, she's free to chime in about any random thing. When red is showing, it needs to be some kind of emergency. This has help us maintain domestic peace.
The shape and color of the dots borrowed from Brazilian steak houses where they have markers used to indicate whether the people serving various cuts of meat should stop by your table.