If you have a timber front door — particularly on an older or period property — you may have both a deadlock and a nightlatch fitted, or just one of the two. Understanding the difference matters for both your day-to-day use of the door and for meeting your home insurer's requirements. Here's a plain-English guide to what each one does and when you need both.
What Is a Nightlatch?
A nightlatch — commonly called a Yale lock after the most well-known manufacturer — is the spring-loaded latch typically mounted about two-thirds of the way up the door. It has a large round cylinder on the outside (where your key goes) and a small knob or lever on the inside that you use to open it from within.
The key characteristic of a nightlatch is that it operates automatically: when you pull the door shut, the spring-loaded latch clicks into the keep on the door frame without you needing to do anything. This makes it very convenient — you just pull the door behind you and it's latched.
However, a nightlatch only provides a single locking point, and in its most basic form the latch can be slipped open — pushed back with a credit card or similar tool — if the door frame doesn't fit tightly. British Standard nightlatches (those meeting BS3621) have a deadlocking function that prevents slipping, but even then they provide only one point of contact between the door and frame.
What Is a Deadlock?
A deadlock is a lock that requires a key to both lock and unlock it — there is no spring-loaded mechanism. The bolt extends into the door frame only when you turn the key, and it can only be retracted by turning the key again. It cannot be slipped, sprung, or manipulated without the key or significant force.
The most common type on UK timber doors is the five-lever mortice deadlock — set into a pocket (mortice) cut into the door body, with only a keyhole visible on the face of the door. Five-lever refers to the number of levers inside the lock that must be aligned by the correct key before the bolt will move. The relevant British Standard is BS3621, which requires a minimum of five levers along with various anti-tamper and anti-drill features.
The Key Difference in Security Terms
A nightlatch secures the door against casual entry — someone pushing or pulling the door open. A deadlock secures the door against forced entry by throwing a solid bolt deep into the door frame.
Neither alone is considered adequate security by most home insurers. A nightlatch alone can be defeated too easily. A deadlock alone is inconvenient because you must use a key every single time you enter or leave — including in an emergency. The standard approach for a timber front door in the UK is both: a nightlatch for day-to-day convenience and a five-lever mortice deadlock below it for proper overnight and away-from-home security.
What your insurer almost certainly requires: Most home insurance policies that reference door security on timber doors specify a five-lever mortice deadlock meeting BS3621. A nightlatch alone — even a British Standard one — is usually not sufficient on its own to meet policy requirements on a main external door. Check your policy documents for the specific wording.
How to Tell What You Have
Stand at your front door from inside. If you can see a round cylinder about two-thirds up the door with a small knob below it, you have a nightlatch. If you can see a keyhole set into the door itself — often below the nightlatch — with no visible lock body, you have a mortice lock set into the door. If you have both, you're set up correctly.
Open the door and look at the edge. A mortice lock will show a rectangular faceplate set into the door edge with the bolt visible. The faceplate may have BS3621 stamped on it — if so, it meets the British Standard. If there's no marking, or if there are fewer than five levers (you can usually tell from the key profile), it may be a basic lock that doesn't meet insurer requirements.
Upgrading Locks on a Timber Door in Stourbridge
If you have a timber door with only a nightlatch, or with an old mortice lock that doesn't meet BS3621, AMP Lock can advise and carry out the upgrade. We cover Stourbridge, Halesowen, Dudley, Kingswinford, Hagley, Kidderminster, and all surrounding areas. Call or WhatsApp on 07961 169 681 — no call-out fee, and pricing confirmed before we start.