What a 'Do Not Duplicate' Stamp on a Key Really Does

A 'do not duplicate' stamp on a key does not stop anyone from copying it. The stamp is a printed request. It changes nothing about how the key is cut or what the lock accepts, so anyone with the right blank and a key machine can make a working copy. Real limits on copying come from the key and lock system itself, such as a restricted keyway.

The stamp changes nothing about the key or the lock

A key works because of its shape. The blank, meaning the uncut piece of metal, has grooves along its side that must match the keyway, the shaped slot in the lock cylinder. The cuts along the edge line up the pins inside the cylinder so it can turn. A key machine reads those cuts and traces them onto a new blank.

A stamp is letters pressed into the bow, the flat part you hold. The machine never reads the bow. The lock never sees it. A stamped key and an unstamped key with the same cuts open the same door, and a copy of either works as well as the original.

What a 'do not duplicate' stamp is meant to do

A 'do not duplicate' stamp is a notice. It tells whoever holds the key, and whoever is asked to copy it, that the owner does not want copies made. For a landlord or office manager, the stamp puts that wish on the key itself instead of in a memo nobody reads.

Any effect depends on the person at the key machine choosing to honor the notice. If that person ignores it, the machine cuts the copy exactly as it would for any other key. The stamp has no connection to the lock, so nothing changes on the door side either way.

A stamped key also keeps no record. It gives no sign of how many duplicates already exist or who has them.

Is a stamped key the same as a restricted key?

No, and this is where most of the confusion sits. A stamped key is an ordinary key with words on it. The blank is common, so getting a copy is mostly a matter of finding someone willing to cut it.

A restricted key system works differently. Its keyway has a profile that is not sold as an everyday blank, so the blanks themselves are harder to get. Copies are usually ordered through a controlled channel that checks the request against a record of who is allowed to ask, often tied to an ID number or card. Many high-security systems also add features the cylinder checks for beyond the usual cuts, so an ordinary blank cut to the same pattern will not turn the lock.

A restricted system is a real barrier, though not an absolute one: it makes unauthorized copies much harder to get, not impossible. The difference is mechanical. The stamp asks. The system restricts.

When the stamp is enough, and when it isn't

A stamp is a reasonable reminder when the stakes are low and you know where every copy is, such as a spare kept by a family member. Keeping the label does no harm, and it sets an expectation for whoever holds the key.

The stamp stops being enough once you can't account for every copy. These situations usually call for something more:

• Staff turnover, especially when keys went out without a sign-out record
• Past tenants who held keys during their lease
• Contractors, cleaners, or dog walkers who had a key for a while
• A lost key, or one that was out of your hands long enough to be copied

When old copies may be out there, rekeying the cylinder changes which cuts it accepts, so the old keys no longer turn it. A restricted or high-security system handles the next round by making new copies harder to get. Access control with cards or codes takes a different route and lets you remove one person's access without touching anyone else's.

Whichever way you go, keep a simple record of who holds which key and when each one came back. That record does more than any stamp. To talk through which approach fits your door or your building, call NoMad Locksmith & Security at (917) 337-9703.

Frequently asked questions

If my key says 'do not duplicate', should I still rekey after a tenant or employee leaves?

Yes, if you can't confirm that every copy came back. A 'do not duplicate' stamp neither prevents copies nor shows whether any were made. Rekeying changes the pins inside the lock cylinder so the old keys, originals and copies alike, no longer turn it. New keys can carry the stamp as a reminder, but the rekey is what shuts out the old ones.

How can I tell whether my key is on a restricted system or just stamped?

A key that is only stamped looks like any common house or office key with words added to the bow. Keys on a restricted system often carry an ID number and an unusual groove pattern, and copies come through whoever manages the system. A number alone is not proof. The person who set up the locks, or a locksmith looking at the keyway, can tell you which kind you have.

Does a stamped key make a lock less secure than an unstamped one?

No. A 'do not duplicate' stamp has no effect on the cuts, the blank, or the lock cylinder, so the lock is equally secure either way. The real risk is indirect. A stamped key can make an owner feel protected and skip rekeying after a key goes missing or someone leaves. Treat the stamp as a note, not as a reason to skip that step.

What are the practical ways to limit who has copies of my keys?

Limiting key copies starts with knowing who has each one. Number your keys, write down who received each key and when, and collect it when that person moves out, leaves the job, or finishes the work. If the count ever comes up short, rekeying shuts out the missing keys. For tighter control, a restricted keyway makes blanks harder to get than a stamp ever could.