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Should door locks and deadlocks be keyed the same. Is there any advantage or disadvantage (besides having more then one key) in having them keyed different?

closed as primarily opinion-based by isherwood, ThreePhaseEel, The Evil Greebo, Tester101 Jun 28 '17 at 13:06

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    Six on the one hand, half-a-dozen the other. – Ecnerwal Oct 23 '15 at 14:04
  • as Ecnerwal eloquently stated it's about simplicity. The place of purchase should key them the same at no charge. – ojait Oct 23 '15 at 15:39
  • Yes. No additional security from 2 different keys be +1 additional hassle. Two keys to keep track of, two keys to replace, two keys to fumble with while holding kids, bags of groceries. Been there, done that. Key them the same. You'll thank yourself. – JS. Oct 23 '15 at 22:31
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The big disadvantage is having to keep two keys with you instead of just one. If you lose your keys (or someone steals them) both keys are compromised so there's not an advantage to having two different keys in that case.

The only advantage I can see is if you frequently need to let other people into your house. You could hide the door knob key or give it to the third party, and on the day when they need access leave the deadbolt unlocked. That way the door is still locked and the third party only has access when you allow them to. Any other time the deadbolt will be locked so even if someone finds the hidden key they can't use it.

It's a bit contrived, but using the two keys as a "double lockout" type scenario is the only advantage I can come up with.

  • With the visitor scenario, how is this different from hiding both keys? – jqning Oct 23 '15 at 16:30
  • @jqning if someone finds one key, they can't get in. They need both keys. I was thinking that you would always have one key hidden outside, and when you needed someone to get in the house, you would just leave the knob unlocked and tell them where the key was. It's a weak premise. – JPhi1618 Oct 23 '15 at 16:34
  • but that doesn't seem like the two keys offers an advantage over one key. In either case a person has access to your house based on one piece of information - the location of the hidden key or keys. The better point is that you hide the two keys in two locations and tell the visitor the location of both. An intruder who is searching for keys will need to do twice as much work. In that case, have six locks. Or ten! – jqning Oct 23 '15 at 16:39
  • The other disadvantage is if one of your keys fails you are locked out. I know this happens with one keyset but now you have double the chance. Another is if a guy with a mask and chainsaw is chasing you, it will be hard to get inside in time. A person with two different keys definitely gets killed off first. – DMoore Oct 23 '15 at 18:56
  • @jqning The way the visitor solution would make sense to me is if you were able to give the visitor one key in advance but were worried they might copy it (although if you don't trust them to not do that, you've got other problems). You could then only set that lock, and leave the one they don't have a key for unlocked. That would let them in when you want to let them in; but prevent them from getting in at other times if they surreptitiously copied the key you gave them. – Dan Neely Oct 23 '15 at 19:00
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As with most security questions, this one can be answered with an XKCD comic. Essentially, you're making it complicated for someone who is playing by the rules (EG: Someone who will use keys to unlock the door, or try and manually pick the locks). The people who will break the rules will probably go the easier route of breaking your windows, or using some other easier point of access (Like hitting you with a wrench and taking your keys). A system (house) is only as secure as it's weakest point of entry, and taking time to secure an already reasonably secure point of entry does little to improve your security position.

Note: There may be other less security related advantages, but security is not an advantage of differently keyed locks.

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    "Locks won't stop a thief. They just keep honest people honest." – JS. Oct 23 '15 at 22:31
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In my former home, I had the standard knob lock and deadbolt keyed differently. When we had our pest control service visit, I left the deadbolt unlocked and put the key for the knob lock in a combination lock box hanging from the front door knob. The service tech accessed the knob key from the lock box, let himself in to do his thing and then left the key on the dining room table and locked the door behind him. While I trusted the service tech, even good people can go bad and if he decided to make a copy of my key one day, it wouldn't do him any good because I always use the deadbolt. In fact, outside of this service day, I kept the knob lock unlocked and only used the deadbolt. The dual key setup worked for me.

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