The app holds a secret thing. You ask yes-or-no questions out loud, the passenger taps the one you asked from the list, and the app answers -- then says what share of the remaining candidates your question ruled out and what the best question available would have ruled out. Name the thing inside the question budget to clear the round.

Players: Two or more people in the car.

Driver: Asks the questions. The phone answers, so nobody argues.

The bar: The questions its own best-split strategy would need on the things in play.