Quiet Boxes are a simple and elegant, strange and glossy black cabinet with gold trim is a miniature prison for one. The only way to release a captive from its velvety purple interior is to put another prisoner inside. It is said that the quiet box causes its prisoners to lose their grip on reality. Those placed inside can neither see, hear, nor smell anything. after a prolonged imprisonment, a captive feels unnaturally relaxed, eventually loses all sensation, and is left unable to think clearly when released.
The quiet box was a specialized prison cell usually reserved for extremely dangerous, and powerful beings. There are two mentioned in the series: The one at Fablehaven, and another at Living Mirage. Both of them contained, for a long time, Navarog, the Black Dragon, and Nagi Luna, an extremely powerful and evil Demon respectively. Eventually, however, each of them was emptied of their prisoners, and were then inhabited by a Narcoblix, and a Human, respectively.
Another Quiet Box is located in the dungeon of Stormguard Castle. It once held the criminal Jasmine Oxgard, but later, it changed to one of the three brothers of the castle, Lockland. Now, Seth and Kendra's housing Knox is there.