No. Locksmiths can duplicate any key with such markings, provided that the locksmith has the key blank to cut.

Therein lies the “rub.” You have to have the key blank that matches they key you want to copy. Although I and most other locksmiths routinely sell KW-1 (Kwikset pattern) and SC-1 (Schlage pattern) keys, among others, using blanks that are marked “do not duplicate,” anyone with a corresponding blank can copy these keys.

But usually, when you see a “DND” marked key, it means you cannot duplicate it, as in, you are unable to procure the correct key blank. In this case, “DND” means you can’t copy this key even if you wanted to.

Many keys marked “do not duplicate” are what is referred to as restricted keys. The pattern of these keys (and their corresponding locks) are sold only to specific locksmiths; these locksmiths have purchased a “license,” so to speak, by purchasing a specified amount of a certain key and/or hardware from a lock manufacturer. The manufacturer/distributor essentially agrees not to sell a certain pattern of a key design in a certain geographic area if the locksmith initially buys an amount of hardware. This informal agreement is more or less perpetual. A good example of this are the MX series of locks and keys, manufactured by GMS. I’m not sure, but I think there are about 4 or 5 (maybe more) different designs in this series. My company is licensed a certain MX pattern (one of the first things I “bought into” when I started this company way back when). Other lock manufacturing companies, such as Corbin-Russwin, Medeco, and several others also make restricted keys.

There’s no specific requirement, so what if a locksmith in my town is suddenly licensed the same restricted key pattern that I am using? I’ve often thought about this, but I don’t think it would be a big problem. That hypothetical locksmith would not duplicate a key that he/she is not familiar with (I know I wouldn’t). Restricted keys are a big deal; we record the key bitting and the number of keys issued to our customers. If someone approached me with the same MX key I sell and asked me to duplicate it, I would ask their name, and I would examine the bitting (aka, the cuts) on the key, and then look in my log book to see who has that key (and the authorized parties). If that key is not in my log, that means it’s in someone else’s log; I would not duplicate it. Purchasing a restricted key pattern and/or hardware requires some sort of monetary investment; it’s not something anyone would do. It’s locksmith specific, and even then, it’s specific to a real locksmith business, not some fly-by-night outfit. That’s my reasoning, anyway. Could some rogue locksmith, in possession of the matching key blank, duplicate another locksmith’s key pattern? Sure, but not likely. Not likely at all. Not only is it unethical, but there’s no money it.

Why would someone have a standard Kwikset key, that anyone could copy, marked DND (do not duplicate)? Maybe they can’t afford to re-fit all their locks to a bona-fide restricted key pattern, so they just had their locksmith use these really nice looking key blanks (that have a big square head, marked DO NOT DUPLICATE) cut for them. 90% of the time, no one will duplicate these keys. Your kid at Lowes, or Ace Hardware, or wherever, will immediately assume they can’t legally duplicate the key; they will immediately assume they don’t have that key blank, anyway. Would a locksmith duplicate such a key? Maybe, maybe not. There is no law against it, though.