Are you two aware there are DMs and play groups that DOESNT WANT their game to hand out ato-detection as a game feature at all?
I mean, this is a legitimate problem.
A reply like "let them spot everything at all times" is flippantly dismissing the OP's entire reasoning. You can do better.
Sorry I am not obligated to give every possible solution. I gave my best answer. The OP can use it or not.