• Most bridge bids fairly much mean what they say.  If you open 1♥  then you have enough strength to open the bidding and some Hearts.  Some people play that they must always have 5♥s and some only need 4♥s, but both are regarded as Natural bids.
• Some bids do not mean what they seem to say.  A 2♣ response to partner's 1NT opening is for most people Stayman. It asks about partner's holdings in the major suits and says little or nothing about responder's hand.  This is called a Conventional bid.
• To avoid people being confused about what bids mean, most conventional bids must be Alerted, but some of the most common bids (both conventional and natural) are Announced.

• When you make a call which must be Announced, your partner immediately makes the appropriate announcement.
• When you make a call which must be Alerted, your partner immediately displays the Alert card to both opponents.  Nothing is to be said.
• Some calls must be Announced, some must be Alerted and for most natural calls you do nothing.  You never both alert and announce.

A number of the most common bids must be announced by the partner of the playing making the call.

• Natural 1NT Opening Bids
  • A 1NT opening bid is normally natural, but different people play many different ranges of strength.
  • When your partner open 1NT you must announce your agreed strength range (e.g. "12-14" or 15-17"). 
  • If you might open 1NT with a singleton, your should add "may contain a singleton" or "may contain a singleton club" or whatever is your agreement.
  • A 1NT opening which might contain a void is not regarded as natural and must be alerted.
• 1NT Overcalls
  • A 1NT overcall should neither be announced nor alerted.
• 2NT Natural Opening Bids
  • When your partner open a natural 2NT you must announce your agreed strength range.
  • The expectation of a balanced hand is less with a 2NT opening, so do not give information about singletons in the announcement.
• Stayman
  • If you open a natural 1NT or 2NT and your partner bids 2♣ or 3♣ respectively and it means Stayman, asking about 4-card majors, you announce "Stayman".
  • It does not matter whether you play that Stayman promises a 4-card major or not. You still announce "Stayman".
  • If there has been interference by the opposition, Stayman is alerted, not announced.
  • Opposite a natural 1NT or 2NT overcall, Stayman is alerted, not announced.
  • If the Stayman you play asks about 5-card majors, it is alerted, not announced.
  • A diamond response to an announced Stayman (meaning opener has no 4-card major) is implied by the Stayman announcement and so need no additional action. A heart or spade response is natural as you are showing at least 4 of them.
• Red Suit Transfers (Diamonds to Hearts or Hearts to Spades)
  • If you open a natural 1NT or 2NT and your partner makes a red suit transfer bid (♦ or ♥), you announce "Hearts" or "Spades" respectively.
  • Normal completion of a transfer is implied by the transfer announcement and so needs no additiional action unless it conveys some additional information.
    • For example, if you always jump a level if you have a maximum NT opening and 4 cards in partner's suit, then if you do not jump a level you are denying that type of hand and so the "normal" completion of the transfer would need to be alerted.
  • If there has been interference by the opposition, transfers are alerted, not announced.
  • Opposite a natural 1NT or 2NT overcall, transfers are alerted, not announced.
  • If you play transfers which do not promise at least 5 cards in the suit indicated, they are alerted, not announced, and if asked you explain, for example "transfer to spades, may be only 4 cards".
• Prepared or Short 1♣ or 1♦ Opening Bids
  • Short club openings are often played in 5-card major systems.
  • These short opening bids should be announced, e.g. "May be as short as 2".
• Natural 2-Level Suit Opening Bids
  • These bids must show at least 5 cards in the suit bid.
  • The strength range of the bid is announced, one of "Strong, forcing", "Strong, non-forcing", "Intermediate" or "Weak".
  • Wide-ranging bids may combine these categories, for example a 6-12 opening would be "weak to intermediate".
• Conventional 2-Level Opening Bids
  • Acol 2♣ and Benji 2♣ or 2♦ opening bids are conventional and should be alerted.

When an alertable call is made, the Alert Card is shown to both opponents by the partner of the playing making the alertable call.

Bids and Passes

• The principle of alerting is that any bid or pass up to 3NT, which is not announceable and is either not natural, or is natural but has some potentially unexpected meaning, should be alerted.
• In the first round of bidding (i.e. ignoring initial passes, so the first bid and the next three calls) conventional suit bids are alerted even above 3NT.  A common occurance of these is splinter bids.

Doubles

• A double of a natural suit bid (i.e. one which shows the suit bid) must be alerted if it is not for take-out (including minor suit openings which may be short).
• A double of a conventional suit bid (i.e. which does not show the suit bid, for example a transfer) must be alerted if it does not show the suit bid.
• A double of a NT bid must be alerted if it is not for penalties.
  • NOTE: In the sequence 1♥ - Pass - 1NT - X, if the X is for takeout of the opening suit, then it must be alerted as you are actually doubling the 1NT even though the meaning in based on the 1♥ bid.

Specific Cases

• 2-Level Opening Bids
  • All 2-level opning bids are either Announced or Alerted. There are no 2-level opening bids which do not need one or the other.
  • Natural 2NT openings and natural suit openings (strong, weak or intermediate) are all Announced
  • Conventional 2-level openings (Acol 2♣, Benji 2♣/2♦, Lucas 2s, etc) are all Alerted.
• Stayman
  • If the Stayman you play asks about 5-card majors, it must be alerted, not announced, as must the responses.
  • If there has been interference by the opposition, Stayman must be alerted, not announced.
  • Opposite a natural 1NT or 2NT overcall, Stayman must be alerted, not announced.
• Red Suit Transfers (Diamonds to Hearts or Hearts to Spades)
  • Normal completion of a transfer which denies the agreed conditions for you to break the transfer must be alerted.
    • For example, if you always jump a level if you have 4 cards in partner's suit, then if you do not jump a level you are denying 4-card support and so the "normal" completion of the transfer would need to be alerted.
  • If there has been interference by the opposition, transfers are alerted, not announced.
  • Opposite a natural 1NT or 2NT overcall, transfers are alerted, not announced.
  • If you play transfers which do not promise at least 5 cards in the suit indicated, they are alerted, not announced, and if asked you explain, for example "transfer to spades, may be only 4 cards".
• Strong Artificial 1♣ or 1♦ opening bids
  • These artificial opening bids must be alerted.
• First-Round Splinters
  • Because first-round conventional suit calls at any level must be alerted, responder splinters must be alerted even above 3NT, but opener splinters are only alerted below 3NT.