I have a Vachette lock installed on a door with a internal doorknob and no doorknob outside (one needs the key to open it). The lock is certified, which means that it is supposed to "resist to attacks" for a given time.

My question is whether this resistance applies only when the lock is turned (ie. the deadbolt is engaged into the frame of the door) or does this also applies to the latch bolt?

In other words, is a door closed, but not locked, conceptually as difficult to open as when the deadbolt is out? I am strictly asking about the difficulty to manipulate the lock so that the latch bolt is pulled in (to open the door) compared to the difficulty to bring the dead bolt in (and, ultimately, the latch bolt to open the door).

  • 1) Certified by who, how? 2) Without seeing that particular piece of equipment and how it's installed, the only answer I can give is "it depends". – keshlam Aug 12 '15 at 22:22

For locks, you have ANSI grades 3-1. 3 being the weakest and 1 being the strongest. Typically, if you buy them as a set both lock cylinders will have the same grade. But the cylinder is only one part of the security. A higher grade cylinder will resist picking and drilling but have no bearing on resisting blunt force to the door. Blunt force is typically the easiest way to open a locked door.

This is where latches and bolts greatly differ. The door latch will not resist someone kicking in the door. A deadbolt has a chance if the door, strike plate and jam are up to the challenge. If you have a metal clad door, an ANSI class 1 strike plate (properly installed with long screws that go into the door framing) and a reinforced door jam it will take a battering ram to open the door.

  • Thank you. By "both lock cylinders will have the same grade" do you mean that picking the lock to open the latch bolt is as difficult as picking it to open the dead bolt? In other words, greatly exaggerated, it is not like a screwdriver would open a latch bolt and the "high security" of the lock would come (be relevant to) the dead bolt only (strictly from a lock picking perspective). I am aware of all the other elements (brute force, cutting the door open, kicking out the hinges, ...), I am looking at the lock picking part only. – WoJ Aug 13 '15 at 6:20
  • Most of the time, manufactures will use the same cylinder for both. Doesn't mean they always do, but usually it cost them less money by making the assembly line simpler. If they use the same key and it appears the metal used for the cylinder is the same, then they are probably the same (but not a guarantee). But the only way to really be sure is to contact the manufacture or ask a really knowledgeable locksmith with experience in that lock set. – diceless Aug 13 '15 at 16:12

It is not uncommon to see a grade 3 knobset packaged with a grade 2 deadbolt.

The grading isn't just (or even primarily) pick resistance. It's also resistance to other attacks and durability under extended/frequent use.

Two locks is always more secure than one of those two by itself. If you're concerned enough to ask this question, you want to install and use the deadbolt.

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