Knock knock. Who's there? Better check… then CLOSE IT. DuoDoor is a door-closing reaction game built around the hinge of iPhone Duo. Your phone is the door. Unfold it to peek inside, and if something nasty lunges at you, fold it shut as quickly as you can. Your reflexes are timed to the millisecond. KNOCK. PEEK. FLINCH. Listen. Someone is knocking from inside, and you'll hear and feel every knock. Unfold your iPhone Duo to slowly open the door. A burglar? A raccoon with your keys?