There's also the room in a room concept where one is suspended inside the other. You might add things like ultrasound masking or blocking, too, since it was a k

There's also the room in a room concept where one is suspended inside the other. You might add things like ultrasound masking or blocking, too, since it was a known attack vector. From there, I thought about, but can't recall if implemented, some double doorway with buffer in between so opening a door didn't leak sounds/signals. Open one, go in, close it, and then go through other.