The app hides a code of digits. You call a guess out loud, the passenger types it, and the app reports two numbers back: how many digits you had in the right place, and how many were the right digit in the wrong place. You work back from that. Ask for the guesses so far at any point and the passenger re-reads them. The round is cleared by cracking the code in no more guesses than the app's own solver would need at its worst.

Players: Two or more people in the car.

Driver: Guesses out loud and works back from the feedback.

The bar: The most guesses its own solver would ever need on a code that shape.