Rules & Etiquette
When your partner makes a 'conventional' bid, you must play your Alert card immediately, so that both opponents see it. When you are sure that both your opponents have seen the Alert card, put it back in the bidding box. Do not wait until it is your turn to bid before showing the Alert card! If you do, the opponent on your left is allowed to change his call without penalty in the light of this new information.
If your opponents ask you what your partner's bid means, you must tell them. It may be sufficient to simply name the convention (eg, "Blackwood"), but if they ask then you must elaborate (eg, "He is asking me how many Aces I have").
A conventional bid is one that carries a different meaning to the obvious inference, either in terms of strength (eg, weak two opening) or in terms of suit or distribution (eg, transfers).
If you are not playing with a bidding box, you should alert a conventional bid by knocking on the table.
See also a list of alertable bids