Door and Window Security Standards Explained for Homeowners

BS 3621 is a British Standard covering thief-resistant lock mechanisms, most commonly mortice locks and single-cylinder deadlocks fitted to final-exit doors — the front or back door you lock when leaving the house. To meet the standard, a lock has to withstand a defined set of attack tests, including drilling, levering and manipulation attempts, before it is passed.

Some insurers specify a BS 3621 lock on final-exit doors as a condition of cover. This is not universal, and it varies by insurer and by policy, so it is worth checking your own documents rather than assuming it applies. A lock stamped with the BS 3621 kitemark on its faceplate is the usual way to confirm compliance.

We can fit locks meeting BS 3621, sourced from established ironmongery suppliers, as part of a door repair or security upgrade. We do not hold the certification ourselves — the standard describes the lock, not the carpenter fitting it.

These two schemes apply specifically to euro-profile cylinders, the mechanism inside most uPVC and composite doors. Euro cylinders became a well-known weak point because an unrated cylinder can be snapped with basic hand tools in under a minute, which defeats an otherwise sound door regardless of how strong the rest of it is.

TS007 is a kitemark scheme that rates cylinders and associated hardware using a star system, typically one to three stars, reflecting resistance to snapping, picking and drilling. A cylinder commonly reaches the recognised “3-star” standard either on its own merit or by pairing a 1-star cylinder with 2-star rated hardware such as handles and escutcheons. SS312 Diamond is a separate, independently tested anti-snap certification scheme often referenced alongside TS007 as evidence of enhanced resistance.

For most homeowners, this is the cheapest and most targeted upgrade available: the cylinder can usually be swapped for one meeting TS007 or SS312 Diamond without replacing the door itself. We fit anti-snap cylinders meeting these ratings, sourced from recognised manufacturers, as routine security upgrade work.

PAS 24 is a Publicly Available Specification that tests a complete doorset or window as a single assembled unit — frame, glazing, hinges and locking hardware together — rather than any one component in isolation. The tests simulate forced entry methods such as kicking, shouldering and levering applied to the whole assembly, not just an attack on the lock.

Because PAS 24 describes how a unit was manufactured and tested as a whole, it applies to new doorsets and windows. It is not something that can be retrofitted by upgrading the lock on an existing door — a door with a PAS 24 tested frame and a door with an ordinary frame and the same lock fitted will not behave the same way under attack. Many new-build developments specify PAS 24 doorsets to meet Building Regulations guidance on security.

For a homeowner replacing an entire external door or window, specifying a product tested to PAS 24 is one of the clearer signals of built-in resistance to forced entry. We can source and fit doorsets and windows meeting PAS 24 as part of a replacement project, working from the manufacturer's documentation.

None of the certifications above count for much if the timber around the lock is weak. In practice, forced entries frequently fail at the frame rather than the lock mechanism — the door is levered until the frame splits around the keep, not until the lock itself is defeated. We cover this in more detail in our guide on why a forced door usually fails at the frame, not the lock.

A keep plate is the fitting that the lock bolt engages with in the frame. A well-specified, reinforced keep spreads the load from a forced-entry attempt across a wider area of surrounding timber, rather than concentrating it on a thin strip of wood around a single screw hole. Long-screw hinges, steel reinforcement strips and box-section keeps work the same way: they move the point of failure from a small, vulnerable area to a much larger one.

This is not a formal certification scheme in the way BS 3621 or PAS 24 are — it is a practical, site-assessed measure rather than a kitemark. But the condition and reinforcement of the frame itself often determines whether a door holds under attack, more than the rating stamped on the lock's faceplate.

Taken together, these standards answer different questions. BS 3621 concerns the lock mechanism. TS007 and SS312 Diamond concern the euro cylinder specifically. PAS 24 concerns the complete doorset or window as manufactured. Frame reinforcement concerns what the door is actually fixed into, which none of the certifications directly address.

Understanding the difference helps you ask the right question when buying a lock, a door or a quote: is this testing the lock, the cylinder, or the whole unit — and has anyone looked at the frame it sits in? We fit locks, cylinders and hardware meeting these standards, sourced from established suppliers, and reinforce frames where the existing timber needs it, as part of our home security upgrade work across Berkshire and South Buckinghamshire. We do not hold any of these certifications ourselves — they belong to the products we fit, not to the business fitting them.