SOS Redouble - After an opponent makes a penalty double,
partner's redouble in either the direct or passout seat demands partner find
a more suitable contract to avoid a costly penalty.
Direct Seat Example:
1N - (X) - XX Agreement usually forces 2C.
(1S) - 2C - (X) - XX; Advancer short in partner's suit,
asking for a red suit rebid
Passout Seat Examples:
2D - (X) - P - (P);
Opener needs help, responder asked to bid another suit
Also see Moscow
Bergen Redouble Over Notrump