The Subaural Bomb, is a device created by the Styx that knocks everything in its blast radius unconcious. There's a variation of this technology called Subaural Field, which they put up around the entrances to the Colony to knock out anyone trying to escape. When Oscar Embers pressed a button on the top of the 'trolley' a low tone cut through the air, quickly building in volume. It grew louder enough for the victims' teeth to chatter and then the tone dropped an octave, then another, then several more, until it couldn't even be heard as a rumble.