What Is a Chain Lock Called? | Names by Use & Setting

A chain lock is called by different names depending on its use: a door chain for interior security, a bicycle chain lock for securing bikes, and historically a chainlock when used as a weapon.

For the full breakdown, see our best Chain Lock guide.

What you call it depends entirely on what you are securing. A bike rider, a hotel guest, and a storage owner are all asking about the same basic idea — a metal chain combined with a locking mechanism — but they use completely different names for it. Below is the breakdown by application so you can identify the right one for your situation.

The Name Depends on What You Are Locking

For bicycles and motorcycles, the standard term is chain lock or chain bike lock. For interior door security — common in hotels and apartments — it is called a door chain, security chain, or chain latch. In the UK, the interior device is frequently called a chain latch or snib in Scotland, while US English uses door chain as the standard.

As an improvised weapon, the same concept — a length of chain attached to a heavy lock — is historically called a chainlock or smiley. Technically, the generic name is a padlock with chain or chain padlock, describing the two-part setup of a padlock and separate length of chain.

Construction and Security Differences

The physical build of a chain lock varies significantly by purpose. Bicycle and motorcycle chain locks use hardened steel links, often covered by a plastic or neoprene sleeve to protect the bike’s paint and resist rust. The locking mechanism is usually an integrated padlock, disc lock, or combination lock. These chains are designed to resist hacksaws, chisels, and leverage attacks — thicker and heavier chains offer higher security but lower portability.

Door chains have a much simpler design: a small catch mounted on the door frame that slides into a track on the door itself. This allows the door to open just a few inches for visual verification — the reason hotels call it a “chain door interviewer” — but prevents full entry. They can be broken with enough force and should never be your only lock.

How to Use a Chain Lock Correctly

Using a bicycle chain lock effectively requires more than just wrapping it around the frame. Wrap the chain through both wheels, the frame, and around an immovable object like a lamppost or bike rack. Pull the chain tight to prevent leverage attacks, then close the integrated padlock or insert the key. If the chain has a plastic sleeve, make sure it covers the frame contact points — without it, the chain will scratch your bike’s paint over time.

For a door chain, slide the catch on the door frame into the track mounted on the door. The door will now open only a few inches. To enter fully, slide the catch out of the track from the inside. Never rely on a door chain as your primary lock — the screws that hold it can be forced out with a strong push, and it should always be used alongside a deadbolt.

Five Common Mistakes People Make

The biggest error is confusing a chain lock with a daily-use bike lock. Chain locks are heavy and bulky — they work best for overnight storage at home or work, but a U-lock is far more practical for frequent street parking during the day. Another frequent mistake is buying a door chain and expecting high security; it is a visual deterrent, not a barrier against determined force. For bike owners, failing to use the plastic sleeve on the chain will scratch the frame over time. Cable locks are weaker than chain locks against heavy cutters, so if you lock a bike in a high-crime area, a hardened steel chain is the safer choice. Finally, avoid trying to source old “chain key locks” — the type with a flexible snake-like key inside a sleeve — as these are obsolete and no longer commercially available; local locksmiths generally do not stock them.