Do Not Duplicate Keys: What the Stamp Really Means

The short answer

A Do Not Duplicate key is a normal key with a request stamped on it. The words ask the person at the key machine not to make a copy, but on an ordinary key blank they do not stop anyone. In the US there is generally no law that makes it illegal to copy a key only because of that stamp. The Associated Locksmiths of America, the main trade group for locksmiths, advises its members to treat a key stamped this way like any other unrestricted key, and it tells owners who want real control to use a patented key system instead. If you need keys that truly cannot be copied at a hardware store, the answer is a restricted key system. In Milwaukee a high-security cylinder with restricted keys starts at $149, and a copy of a standard house key starts at $10.

Why the stamp does not stop copies

The shape of a key blank decides which machines and which blanks can copy it. Most house keys use a handful of common blank shapes that every hardware store, key kiosk, and locksmith stocks. Stamping words on the bow of such a key changes nothing about its shape. Anyone who decides to ignore the words can copy it in a minute. The key kiosk company KeyMe, for example, says it follows the trade group's policy and handles these keys like any unrestricted key.

That is why the trade group has called the stamp misleading for owners: it can make a landlord or a manager feel the keys are under control when they are not.

Is it illegal to copy a Do Not Duplicate key

For an ordinary key, usually not. The stamp is a request from the owner, and it creates no law by itself. A few states have laws about copying keys to public buildings without permission, and California is one example, but those laws come from the state, not from the words on the key.

Patented keys are a different matter. When the shape of a key blank is protected by a patent, only the patent holder, or a company it licenses, may make blanks with that shape. Making or selling those blanks without permission can lead to a patent lawsuit. That legal protection is what gives a restricted key system its strength.

What we do with a Do Not Duplicate key

We treat the stamp as the owner's wish. For a key stamped Do Not Duplicate, we ask for proof that you own or manage the property, or a written okay from the manager, before we cut a copy. That way a copy goes only to the person the owner meant to have one. Our page on key duplication explains how a regular copy visit goes.

How real key control works

Real key control comes from the key and the lock, not from a stamp. There are a few levels.

A restricted keyway uses a blank shape that the maker sells only to locksmiths it chooses, and only for systems they set up. A hardware store cannot get those blanks, so it cannot copy the key.

A patented key adds legal protection to that shape. Patents usually last about 20 years, and once a patent runs out other companies may start making blanks. That is why makers keep releasing new patented key designs, and why an old restricted system may need an upgrade over time.

A key card or an owner's list closes the loop. With most restricted systems, a copy is cut only when the owner shows a card or signs a request, and the locksmith keeps a record of who received each key.

Restricted keys usually go into high-security locks, which also resist picking and drilling better than a standard cylinder. A high-security cylinder starts at $149.

For landlords and businesses

A building with many keys needs a plan more than a stamp. A master key system lets each tenant or employee open only their own door while the manager opens every door, and it starts at $45 per cylinder. Restricted keys stop extra copies of those keys. A simple key log, with a number stamped on each key and a list of who holds it, shows which keys are missing when someone leaves.

When a key does not come back, the only fix is to rekey the locks it opened. Landlords can read our checklist to rekey between tenants and how we handle that work for property managers.

For tenants with a stamped key

If your apartment key is stamped Do Not Duplicate, the simplest way to get a spare is to ask the manager. Many leases limit how many keys a tenant can have, and some buildings use restricted keys that only the manager can order. If the manager agrees, a written okay lets us cut the copy. If the building uses a restricted system, the copy comes through the manager and the locksmith who set up that system.

If you are locked out and your only key is stamped, our page on being locked out of an apartment explains what to do first.