The Intent of the law is basically to "childproof" the gun ! As Tracy-sensei explains now we have to worry about the criminal aspect as well i.e., a child gets hold of an unlocked and gun and kills himself or another , you are going to prison as the gun owner !
If the unlocked gun gets stolen by burglars and it injuries someone , the law is not yet clear on the criminal liability of the owner ! [ when you report your gun stolen to the police " of course it had a lock" ] !
If the gun is under your control , i.e., carried on the person or at home with you , it needs not be locked ! If you leave guns at home unattended , they must be locked !
Many locks on the market ! Good ones share a key in common ! About $ 10 !
Locked or unlocked , if someone uses your gun to injure themselves or others , you will face civil suit !!