Zombies can hear you

I dreamt I was in a zombie game tonight, so in honor of that, here's a custom move that should be easily applicable across systems.

When the characters are in the middle of a zombie apocalypse and trigger a loud noise, roll 2d6 and add it to their noise factor. Your noise factor starts at 0. When your noise factor hits 21 or more, reset it to zero and the characters attract a large number of hitherto undiscovered zombies that were feeding, resting or hiding nearby.

("Loud noise" is not subject to GM whim. It's either the result of an intentional and deliberate action (shooting a gun, blasting some music on loudspeakers) or the result of a failed roll.)