"BS3621" is one of those phrases that appears in insurance small print and on locksmiths' price lists, often without explanation. Knowing what it actually means stops you buying a lock you did not need — or claiming on a policy only to find a condition you missed.
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What BS3621 actually is
BS3621 is a British Standard for thief-resistant locks. In plain terms, a lock that meets it has been tested against a defined set of attacks and requirements — the sort of forcing, drilling and manipulation a burglar might use — and has passed. It is a specification, not a brand or a badge you can buy.
You will normally see it on traditional mortice deadlocks and sash locks, which is what most timber front and back doors still use. Modern uPVC and composite doors use multipoint locking, which is covered by different standards, so a "BS3621 lock" is not automatically the right answer for every door.
When it matters to insurers
Here is the part people get wrong: not every policy requires BS3621. Many standard home policies simply ask that external doors are locked and windows secured when you are out or asleep. Some policies — and this is more common for higher-value contents cover, or for specific named items — do state that the final exit door must be secured with a lock to a particular standard such as BS3621.
The only reliable way to know is to read your own policy wording, or ask your insurer directly and keep their answer. Do not take a locksmith's word for what your policy requires, and do not assume the strictest standard applies if it does not.
How to check what you already have
- Find the lock's faceplate. On a mortice lock, this is the metal strip on the edge of the door, beside the latch.
- Look for a mark. British Standards marks usually show a kitemark plus the BS number, or a European EN 12209 marking. They may be small and faintly stamped.
- Check the whole door, not just the lock. A good lock in a flimsy door is not much protection. Door construction, frames and hinges matter too.
- If in doubt, ask for it in writing. A locksmith can identify the lock and confirm in writing what standard if any it meets.
If you do need to change a lock
Ask for a lock that meets the standard your insurer actually requires and no more than that, unless you want the extra security for its own sake. Keep the receipt and any documentation, because you may be asked for it if you ever claim. And remember that the standard is only one part of security: a decent door, sound frames, and the habit of actually locking up matter just as much.
Common questions
Do I need BS3621 locks to get home insurance?
Not always. Many policies simply require that external doors are locked and windows secured. Some policies, and many for higher-value contents, specifically require a BS3621 lock on the final exit door. Read your policy wording or ask your insurer rather than assuming.
How do I check whether my lock is BS3621?
Look at the lock faceplate or the visible edge of the lock on the door edge. A kitemark and a BS number, or a European EN 12209 marking, is usually stamped or printed there. If you cannot see one, or you are unsure, a locksmith can identify it.
Does BS3621 apply to uPVC doors?
BS3621 is mainly written around traditional mortice locks. uPVC doors use multipoint locks, covered by different standards. If your insurer asks for a certain standard on a uPVC door, check the policy wording and confirm the right specification before buying anything.