A low level reverse is one such as (uncontested) 1-1-2. The 2 bid shows extra values, as it forces partner to the three level if he wishes to put back to clubs. However, as partner has only responded at the one level it clearly cannot be game forcing (though should be forcing). In contrast, 1-2-2 should be game forcing, as if partner has enough to bid at the two level it is unlikely that you will not want to go to game.
There are four low level reverse auctions, the other three being 1-1-2, 1-1-2, and 1-1-2. The problem in these auctions is to distinguish when you wish to go to game or not. Playing standard methods, if it starts 1-1-2, then 2, 2NT, and 3 would be taken as non-forcing, thus showing a weak hand, with every other bid as game-forcing. If you want to agree clubs with a strong hand you cannot simply bid 3, you must either jump to 4, or go via fourth suit forcing, potentially creating a much more murky auction.
To get round this problem, you may have heard people mention 'Lowest of fourth suit and 2NT is bad'. What this means in the sequence 1-1-2 is that ALL weak hands bid 2, with partner responding in the weakest thing he is prepared to play in, usually 2. The 2 bidder will then pass 2, or bid 2NT, 3 or 3, showing a weak hand wanting to play there in each case. Thus, if instead you have a stronger hand with clubs, you can bid 3 immediately, knowing that partner will not pass you.
If, however, the auction had started 1-1-2 then now 2NT would be the bid for all the weak hands, as 2NT would now be lower than 4th suit. The rest would work approximately as before.
Usually the discussion on these sequences stops at this point, leaving several awkward unagreed sequences. In the rest of this article we aim to cover these sequences, and suggest a modification. One of the key weaknesses of the system as discussed so far is that the opener does little to describe his hand, leaving responder guessing often where he should play the hand. We shall address that point too.
The key is to have some extra weak bids, and to realise that there are only a certain number of different hands that the reverser can have. Thus, when it starts 1-1-2, 2 and 2NT are weak and natural, with 2 being weak with a minor, or fourth suit forcing. Three level bids are natural and game forcing (for example, 3 would show 5-5 majors, as it is hardly worth showing a four card heart suit). After 1-1-2-2 opener bids naturally, with 2 showing three card support. (With two spades opener will usually have an alternative bid, with six clubs or a hand suitable for a NT bid.) This enables you to play in 2 or 3, depending on the better fit, avoiding playing a level higher unnecessarily. (For example, xxx x AQJx AKQxx opposite Kxxxx Jx 10xx J10x would bid 1-1-2-2-2-P, whereas if 2 is bid on all hands, responder would now convert the top spot of 2 into 3, an altogether shakier contract.) There is plenty of room for showing stronger hands with good spade suits, so it is little loss not to be able to bid 2 on stronger hands.
The other three reverse sequences work on broadly similar principles. 1-1-2 and 1-1-2 are pretty much as before, with 2NT being all the weak hands. 1-1-2 has 2 and 2NT as weak, and 2 as weak with a minor or fourth suit forcing.