A double of a low level suit contract asks partner to bid the best of the unbid suits. This type of double is called a takeout double, as opposed to a penalty double double which is made when you think you can defeat the opponents' contract.
Takeout double by the overcaller
- 12+ HCP
- at least 3 cards in the unbid suits
- shortage in the opener's suit
- asks partner to choose the trump suit
Here's a perfect hand for a takeout double. Notice that South has length in all of the unbid suits so that whichever one North chooses will be fine.
A takeout double
This next hand is not suitable for a takeout double. South has plenty of points but without length in spades it's better to defend. Partner's always have the habit of choosing your worst suit when they respond to your double so make sure you have at least 3 card support.
Pass! - it's ok to defend sometimes.
Responding to a Double
If partner doubles then you must bid, even with a weak hand. Bid your longest suit. On this hand you should bid 1♥. Partner is forcing you to bid so you don't promise any points at all. Remember, partner has shown some hearts.
Responding to a takeout double.
As soon as any player makes a bid, the double is cancelled. You don't have to bid this time because East bid. East's bid cancelled the double.
East's bid cancels the double.
On this hand next you should bid 2♥. You would have bid 1♥ even with zero points so you have 9 more than you might have had. Tell partner the good news! It might seem dangerous to jump with a 4 card suit but remember that partner is promising support for the unbid suits. You'll be fine with hearts as trumps.
Jump response to a takeout double.
Double or Overcall
When the opponents have opened the bidding it's important to enter the auction if you can. There are 2 main ways of doing this - a takeout double or an overcall.
Overcall to show a good suit, Double to show a good hand.
On this next hand you have support for the unbid suits and 12 points. You're not sure what suit you would like to have as trumps so you ask partner.
This is a great hand to double with.
This time you an overcall is better. You'd like spades as trumps.
Show your suit!
Double then Bid
A takeout double can also be made with 16+ points, even without support for the unbid suits. A simple overcall in bridge shows a maximum of about 15 HCP but you can double and then bid your suit to show a stronger hand.
How will partner know my hand?
A takeout double normally shows support for all the unbid suits and whatever suit partner responds with should become the trump suit. That's the whole idea of the takeout double in the first place! - get partner to choose trumps. If, after hearing partner's response, the player who doubled bids a new suit then the implication is that player doesn't have support for the unbid suits after all and therefore must have a strong hand.