Bidding When Opponents open 1NT
Disturb Over No Trumps. (DONT)
Very disruptive
When the enemy has opened with 1 No Trump, they now have an array of techniques available (Stayman, Transfers, Limit responses) to optimise the outcome. And the enemy bid is quite pre-emptive if it's a weak NT.
It's time to get your own back. The "DONT" overcall is quite agressive, and clearly requires partnership agreement before being used. (Otherwise your partner will assume you behave more "normally", see 'single suit overcall', or 'Landy' or '0120 Double over 1NT' which describe overcalling when you are somewhat stronger.)
Assuming you agree to use "DONT" against a Weak NT (12-14HCP), then with only 8 points and any two 4-card suits, bid the lower denomination suit, i.e. 2,,. (Note: A bid of 2 shows one 6-card suit and 10HCP).
Another method that some partners agree to use:
- 2 shows any single suit; the partner should bid 2, after which the intervenor corrects to his actual suit
- 2, 2, 2 shows the bid suit and any higher-ranked suit, with clubs as the highest-ranking suit.
Unless the enemy know how to use Lebensohl (nearly everyone doesn't), then you've nicely messed up their systems. And (who knows?) your partner might even have a useful fit.
Alternative bids are possible in this situation, such as a single suit overcall, or 'Landy'. DONT is more disruptive than Landy, since it covers many more situations, and it can use up many of opposition's available bids: 2,,, and even . But it is dangerous, and can land you in trouble.
Vulnerability
Upgrade from 8 to 10 points when vulnerability is unfavourable.
Respond?
Unlike Landy, you don't need to respond, since you know that partner has some cards in the bid suit! After a 2 or overcall, you can find out which is the other suit inferred in the overcall, simply by raising to the next suit up or respectively. Overcaller can then correct.