Remember "The Club" steering wheel lock for cars? There was one for the NES called "Homework First".
It was a 4-wheel 10-position combination lock only. No metal key version. Between covert observation of a parent locking and unlocking it, and just brute forcing the key, I don't think it would have been very effective.
Suppose you can perform one key test per second… You could break it in 2.8 hours while your parents sleep. Only have to do it once.
Actually, scratch that. Make it simply this: "You can use the NES as much as you want. But you have to open the lock yourself."
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