From the outside, they often look like vacant storefronts: The former business’ signs occasionally still hang on the buildings, but now the windows are obscured.

Anyone who wants to get in has to knock first. If you walk by at night, you might hear the slapping sound of people hitting buttons on an arcade game.
Except, they aren’t playing just any arcade game and the prizes aren’t children’s toys. Police say the people inside are gambling—and they’re big business for the operators.