The NES Lockout was a combination lock device made by SafeCare Products, Inc. and Master Lock that featured a "Self-Setting" combination that attached to the open bay of a front-loading NES via a hole under the control deck directly below the chamber lid which enabled the lock to grab the console like a vise to prevent removal. The device was intended to allow parents to keep children from playing an NES when they weren't supposed to.
References
NES Lockout Wikipedia(Text) CC BY-SA