I don't recall if anyone has mentioned them yet, but honestly I was focusing on spells without them for that reason.
Either way, having a focus or component pouch in your hand is all you need. If it was already there all the time, I don't think it would be much of a clue, personally. Now, if it is a cost component--maybe.
Again, not that I recall.
IMO if an item allows you to "cast a spell", then it could be a reaction to you using the item to "cast a spell" to counter it, but I would have to review the wording to see if that would be RAW or not.