This question already has an answer here:
It'll be nice if a notification is displayed when you're writing an answer to a question and someone else votes it as a dupe. Today, I answered a question and when I submitted, I noticed that it's being voted as an exact duplicate. It was indeed a duplicate so I deleted my answer and voted as a dupe. It would be nice to have notifications like the one that says "2 new answers added to the question" for duplicate votes and closing too.