Bulls and Cows, But Four Secret Codes at Once: The QUADLOCK Playbook for 1A2B Number Guessing
If you grew up playing pencil-and-paper number guessing games, you know the drill: someone thinks of a four-digit code, you guess, and the answer comes back as "2A1B" — two digits correct and in the right spot, one more digit present but in the wrong place. The game is called 1A2B in China, Bulls and Cows in the English-speaking world, and it shares its deduction DNA with Mastermind.
A brand-new iOS game called QUADLOCK just took that classic formula and twisted it: instead of cracking one secret code, you face several locked safes at the same time. It launched September 28, 2026, and it's free.
The core idea, in one paragraph
Every locked safe hides a 4-digit code with no repeated digits. Each turn you enter one guess — and every unsolved safe responds with its own A/B feedback at once. A means the digit is correct and in the right position; B means the digit is in the code but in the wrong position. Crack every safe before your queries run out and you win.
That single change reframes the whole game. Your one guess is now a multi-target information probe: four safes, four different reactions. The skill shifts from "solve this code" to "compare the clues across codes and weave them into one deduction chain."
Three board sizes: 2 safes, 4 safes, 8 safes
Two safes is the warm-up — it teaches you why one guess produces two different answers. Four safes is the standard challenge. Eight safes is a full logic marathon, with a screenful of safes reacting to every query.
The real twist lives in the linked-rule levels:
- Some challenges force every code to share one digit. Confirm that shared digit in one safe and half the candidate space collapses in all the others
- Some restrict the available digit pool — your search space gets drawn smaller for you
- Others require every safe to start with a different digit, so ruling out a leading digit in one code can lock it in for another
This is what separates QUADLOCK from a plain number-guessing game: clues flow between safes. Feedback on one lock is raw material for reasoning about the rest.
The last-chance mechanic
Down to your final query with safes still open? If that last guess cracks any single safe, you earn one extra query. A cliffhanger solve genuinely keeps the run alive — which makes every ending a little bit of a heart-pumper.
Three strategy tips for your first runs
1. Front-load information, not luck. Open with digits spread wide — probe guesses like 0123 and 4567 that share no digits. You are not trying to hit a code; you are establishing which digits exist on the board at all. In a multi-safe structure, this maximizes the value of every early query.
2. Watch the candidate counters. QUADLOCK shows how many possible codes remain for each safe. That is your reasoning progress, visualized. If a guess sharply lowers candidate counts across several safes, it was a good question. If nothing moves, the query was wasted — change what you are asking, not just the number you type.
3. Reason across the safes. In shared-digit levels, prioritize the digit that keeps appearing with high A/B counts across multiple safes. In distinct-first-digit levels, cross confirmed leading digits out of every other safe's candidates. At eight safes, cross-safe thinking isn't a bonus — it's a requirement.
A pixel cipher agent and a very commute-friendly pace
A little pixel-art cipher agent reacts to your moves while you play, and the vibe is perfect for those tense last-query moments. Rounds are quick: tap in numbers, read clean A/B feedback, done. A 10-minute subway ride fits a standard 4-safe run comfortably. No account, no internet required — pick it up, put it down.
Every round generates fresh codes, so there is no fixed solution to memorize. You can play in two distinct styles — probe-then-place, or design each guess specifically to separate likely candidates — and both train the same underlying skill: making decisions under incomplete information. That's exactly why logic puzzle games keep getting recommended as brain training.
Who is this for?
- Anyone who enjoys Wordle, Mastermind, or sudoku and wants a new "one round a day" habit
- Logic-puzzle fans who find single-code Bulls and Cows too simple
- Commuters who want a low-friction brain teaser
- Parents and teachers looking for a fun way to practice deduction and elimination
If you have been searching for a 1A2B game, Bulls and Cows app, code breaker, number puzzle, or deduction game, QUADLOCK is likely the most unusual variant of the genre on the App Store right now: one guess, many locks.
Download QUADLOCK on the US App Store → — Free, iOS 17+, English storefront.
Chinese readers: the app is listed as 「1A2B 四重密码」 on the mainland App Store — see the CN store page.
