Proof? I don't know what this means.

In Massachusetts, unless you have a firearm under your "direct control", it has to be locked up, either in a lockable container or with a bolt or trigger-lock. There are severe fines and punishments for not doing so (and for not reporting a stolen firearm), ranging from prison-time to losing your license. Please note that when you buy a firearm, or at least a handgun, in Massachusetts, the seller is legally-required to provide you with a bolt/trigger lock, so it isn't an additional expense on the purchasers part.

You have to do this even if there are no children or roomates in the house. The firearm has to be "non-functional" to any and all non-licensed users

I literally have my rifle hanging on the wall next to me, "ready to go" with the exception of a trigger lock. Said trigger lock would take all of 5 seconds to remove with the key.