http://abfevents.com.au/events/tournreg ... gs2017.pdf
It deserves a full reading. The discussions of announcements, pre-alerts and delayed alerts should be understood and are not discussed further here. But some rules may be difficult to remember or interpret, and to make that easier I have composed a summary of those that I think are most helpful to players.
Do Alert___________________________
Any artificial opening regardless of level
1NT forcing or semi-forcing response
Inverted minor raises
Weak jump responses
3♣ response to 2NT
Trial bids
Pass-or-correct bids
Any artificial opening regardless of level
1NT forcing or semi-forcing response
Inverted minor raises
Weak jump responses
3♣ response to 2NT
Trial bids
Pass-or-correct bids
Do Not Alert_______________________
Non-opening bids above 3NT
Natural 2/1 response forcing to game
Doubles, redoubles, cue-bids
Weak jump overcalls
2♣ response to 1NT without interference
Non-opening bids above 3NT
Natural 2/1 response forcing to game
Doubles, redoubles, cue-bids
Weak jump overcalls
2♣ response to 1NT without interference
For this purpose "cue-bid" means a bid of a denomination that was either bid or shown by an opponent. This includes notrumps, so for example a 2NT overcall of a 1NT opening is not alertable regardless of its meaning.
A "trial bid" is a bid of a new suit as a game try after another suit has already been agreed. For example the uncontested auction 1♥ - 2♥ - 3♣. Regardless of whether 3♣ shows length, shortness or a feature, if it's a game try in hearts then it should be alerted.
There's some uncertainty about the semi-forcing 1NT response. While it is by definition nonforcing, it shares essentially the same attributes as a forcing 1NT response (in particular a higher upper limit of strength than a standard 1NT response), and thus I think merits the same alerting treatment. When in doubt it's better to alert.
And explaining an alerted semi-forcing 1NT should be done carefully as you don't want to start in terms of what you, the explainer, might do. What I suggest is something like "We play 2/1 Game Force so this shows about 6-12 points. It could also have 3-card support for my suit if near the top or bottom of the range."
This summary was prepared with the aid of some feedback from experienced players on the Bridge Winners site.