During the auction: During and before the final pass, any player, at his own turn to call, may request a full explanation of the opponent auction. So even though alerts are not made over 3NT either opponent, at his turn to call, may ask for an explanation of a bid.
Review after final pass: Declarer or either defender may, at his first turn to play, require all previous calls to be restated. Now that we use bidding boxes, the bids should be left on the table until the opponent makes the opening lead.
exceptions to alert
Announcements in the following 3 instances should be made each time the bid is made:
1. When partner opens 1NT , you state the range e.g. "12-14"
2. When partner opens a short or prepared Minor you should state " could be short"
3.When partner bids 2D or 2H as a transfer, you should state "Transfer"
You do not alert a transfer, you announce it by saying "transfer"