Acknowledging a check mate Do you have to tell someone that they set them selves up for a check mate? For example if the queen is guarding the king on both ends and one person moves there queen to the left. Does the opposite person have to tell the opponent that they set them selves up?
If your question is "Do I have to tell my opponent that he just made a move from where checkmate is forced?", the answer is "No", you don't have to tell your opponent he is setting himself up for checkmate. In fact, that is rather the point of the game!

The only times you have to tell anything to your opponent is:


When offering a draw
When you want to adjust a piece.


If your question is "Do I have to tell my opponent that he is in checkmate?", the answer is still technically "No". Even the customary "Check" and "Checkmate" are optional. 

Practically, if your opponent does not grasp that he is in checkmate it may be useful to point that out to him one way or another, and the traditional "Checkmate!" should do the trick.