Do I need both a Yale and a mortice lock on my front door?

Not automatically. A nightlatch provides everyday latching and a mortice deadlock can provide a separate locking point, but the suitable arrangement depends on the timber door, frame, escape needs and any written policy requirement.

How do I know if my mortice lock is BS3621?

Look at the faceplate on the edge of the door. A genuine BS3621 lock will have the BS3621 number stamped on it along with the BSI Kitemark — a heart-shaped symbol. If you cannot see these markings, the lock probably does not meet the standard. Some older locks carry a BS number but not the Kitemark, which means they were not independently tested.

Can a locksmith fit a mortice deadlock to any wooden door?

Not every timber door can accept every mortice deadlock. The exact product instructions, door thickness and construction, existing cut-out, frame, escape needs and any written requirement must be checked before cutting or fitting.

What is the difference between a 3-lever and 5-lever mortice lock?

A 3-lever and 5-lever mortice lock use different lever arrangements, but the lever count alone does not prove certification or suitability. Check the visible marking, exact product, door and frame, then compare the current written policy before deciding whether to replace it.

Yale Lock vs Mortice Deadlock: Which Do You Need?

Compare nightlatches and mortice deadlocks, their different functions, and the door, escape and written-policy checks needed before changing either.

Yale Nightlatch vs Mortice Deadlock: What's the Difference?

Customers across Coventry ask how these two lock types differ. They do different jobs, and some suitable timber doors use both, but the right arrangement depends on the complete door, frame, escape needs and any written policy condition.

The sections below explain what each type does and the door, frame, escape and policy evidence that should be checked before choosing either one.

What Is a Yale Nightlatch?

A Yale nightlatch — often just called "a Yale" — is the lock you can slam shut. It has a spring-loaded latch bolt (the curved bit that clicks into the frame) and sits on the inside surface of the door. The cylinder (where you put the key) pokes through from the outside.

When you close the door, the latch springs into position and the door is held shut. You can open it from inside using the handle without a key. From outside, you need the key.

How a Nightlatch Works

The latch bolt is spring-loaded and bevelled so the door can be pulled shut

A snib on the inside lets you hold the latch back (to leave the door on the latch) or lock it in the deadlocked position

Standard nightlatches can be opened by slipping a credit card or strip of plastic between the door and frame — this is called loiding

Deadlocking nightlatches have a secondary bolt that, when the door is fully closed, prevents loiding

Common Types

Yale 85 — basic rim nightlatch, no deadlock function. Not secure enough for a front door.

Yale 89 — deadlocking version, much better. The small secondary bolt deadlocks the latch when the door is closed.

ERA and Union equivalents — similar products from other manufacturers.

British Standard nightlatches — BS8621 rated versions that can be unlocked from inside without a key (fire safety feature).

What Is a Mortice Deadlock?

A mortice deadlock is a lock fitted inside the body of the door. "Mortice" means it sits in a rectangular pocket (mortice) cut into the edge of the door. "Deadlock" means the bolt doesn't spring — it's thrown by the key and stays locked until you turn the key again.

How a Mortice Deadlock Works

The deadbolt is a solid rectangular bolt, typically 20mm throw on BS3621 locks

Inside, there are five levers — flat metal plates that must all be lifted to the correct height by the key before the bolt will move

The key has a pattern of cuts that corresponds to the lever positions — this is why mortice keys look so distinctive

Once locked, the bolt is designed to resist being pushed or slid back; the exact certified model and complete installation determine tested performance

The BS3621 Standard

The BS3621 standard is the benchmark for mortice deadlocks. A lock carrying this certification has been independently tested for:

Pick resistance

Drill resistance (hardened steel plates protect the levers)

Bolt strength — the bolt resists sawing and forcing

Key security — at least 1,000 key combinations (differs)

The bolt throws at least 20mm

Some home policies name BS3621 for a suitable timber door, while others describe security differently. Only the current policy or insurer can establish the requirement and any effect on cover.

When a Timber Door May Use Both

A nightlatch gives you convenience — you can shut the door behind you quickly, and it latches automatically. But it's not a high-security lock. Even a deadlocking nightlatch can be defeated by a determined intruder.

A mortice deadlock gives you security — once that bolt is thrown, it takes serious force or the right key to open the door. But you have to remember to lock it with the key every time.

The combination of both covers your bases:

The nightlatch keeps the door closed and provides basic security for everyday use (popping to the shops, answering the door)

The mortice deadlock provides genuine security when you leave the house or go to bed at night

The two locks perform different jobs; any policy requirement must be checked in the customer's own written terms

Timber doors in areas such as Cheylesmore, Styvechale, and Earlsdon may have a nightlatch alone, a mortice lock alone, or both. The markings, condition, door and frame need checking rather than inferring performance from appearance or postcode.

Common Misconceptions

"My Yale lock is enough"

A nightlatch and a mortice deadlock perform different roles. Whether another lock is suitable depends on the door, frame, escape requirements, existing hardware and any written policy condition; inspect the complete installation before altering it.

"I don't need a mortice lock because my door is strong"

The strength of the door is irrelevant if the lock can be bypassed. A strong door with a weak lock is like a safe with the combination written on it.

"My lock has 'BS' on it so it's fine"

Not necessarily. Older BS3621 locks may have been superseded, and some locks carry a BS number for a different standard. Look for the BSI Kitemark — the heart-shaped symbol — alongside the BS3621 marking. That confirms independent testing.

"Mortice deadlocks are old-fashioned"

They're traditional, but the engineering is still relevant. A currently certified five-lever mortice deadlock can improve tested resistance when correctly fitted to a sound, compatible door and frame.

When to Upgrade

You should consider upgrading your locks if:

You only have a nightlatch on a timber external door — have the complete door and current policy assessed before adding another lock

Your mortice lock is a 2 or 3-lever type — compare it with a currently certified option suitable for the door

Your nightlatch is a basic non-deadlocking type — upgrade to a deadlocking version or BS8621

You've moved into a new property and cannot account for every working key — consider a lock change

Your locks are visibly worn, stiff, or difficult to operate

Your written policy specifies a lock requirement the current product does not meet

What About uPVC and Composite Doors?

If you have a uPVC or composite door rather than a wooden one, this whole discussion doesn't apply to your door. uPVC and composite doors use euro cylinder locks in a multipoint locking system, and the main concern there is lock snapping. The upgrade path is an anti-snap euro cylinder, not a mortice deadlock.

Prices and What to Expect

Current starting prices for supported lock work are maintained on the prices page. A new mortice cut, a like-for-like replacement, a nightlatch change and a combined scope require different door preparation and products, so they should not share an assumed fixed price.

The existing lock, dimensions, door condition and required certification determine the compatible product and fitting scope. Call 024 7522 4730 so I can confirm the price basis, current product availability and whether the work is likely to need more than one visit.

The Bottom Line

On a suitable timber door, a nightlatch can provide everyday latching while a certified mortice deadlock provides a separate tested locking point. Whether both are appropriate depends on the door, frame, escape needs and written policy; fitting a particular lock does not by itself guarantee cover.

If you're not sure what locks you have, or whether they meet a stated standard, call 024 7522 4730. Check the listed Coventry areas, then provide the exact door and any written requirement for an assessment.

Yale Locks vs Mortice Deadlocks: Which Does Your Front Door Need?