It would be pretty cool if there was some kind of device, not unlike an SIC amplifier in terms of mechanics, which you bolted to a wall. This would make it harder for sound to escape the room, and make it impossible to listen in on the other room.
Of course, make it expensive sure but also, there are lots of uses I could imagine for this. You could put it up in your living room to make sure what's in there stays in there. Or if you have a room one pad that you're using to kidnap someone inside, you could keep them there more viably.
You could also add a timer on it. So it only works for x amount of time before it needs to recharge or be toggled again after an hour or so etc.
BAKALAKA
