QUADLOCK: 1A2B Code Puzzle

One 1A2B guess can reveal clues to crack multiple codes.

QUADLOCK turns the classic 1A2B number game, also known as Bulls and Cows, into a multi-lock logic puzzle. Instead of solving a single secret code, you will work on several safes at once. Enter one unique 4-digit guess and every locked safe responds. Read the clues, rule out impossible combinations, and crack every code before your queries run out.

Easy to learn, satisfying to solve

Each secret code contains four different digits. A means a digit is correct and in the right position. B means the digit is in the code but in the wrong position. A result of 2A1B, for example, means two digits are exactly right and one more digit belongs in a different place. Use each response to refine your next guess.

Solve several number codes together

Choose a 2-safe warm-up, take on the standard 4-safe challenge, or test your strategy against 8 safes. Every guess applies to all unsolved codes, so one carefully chosen number combination can help eliminate possibilities across the whole board. Compare the feedback from each safe and turn separate clues into a larger deduction.

Linked rules change the puzzle

Some challenges make every code share a digit. Others restrict the available digit pool or require every safe to start with a different digit. These linked rules create opportunities to reason across safes: a clue from one code may help you narrow down another.

A final chance to keep going

Crack any safe with your final query and earn one extra query. A last-second solve can give you the opening you need to continue working on the remaining codes.

Follow every clue

Review the feedback history for each safe and see how many possible codes remain. Use the candidate count to plan your next move, practice deduction, and improve your number-logic strategy one guess at a time.

Discovery signals