You should alert
(a) Any call that is a convention
(b) Any bid that is natural but unexpectedly weak
(c) A forcing raise of a natural opening one of a suit.
The following bids are considered natural and do not require
an alert. Any offer to play in a suit named for the first time
(a) Three or more cards in a minor suit
(b) Four or more cards in a major suit and says nothing about
any other suit.
The following conventional bids in common use need not be
Stayman 2 club response to a 1NT opening bid
Strong Acol 2 club opening bid.