In short:
- The three words answer different questions. Deadlock describes how the bolt behaves, nightlatch is a type of surface-mounted latch, and mortice describes how a lock is fitted into the door.
- A sprung latch only keeps the door closed. A deadbolt that has been locked by the key or thumbturn is what actually secures it.
- A nightlatch sits on the inside face of the door; a mortice lock sits in a pocket cut into the door edge. You can tell them apart in a few seconds.
- A door locked by key on both sides is harder to escape through in a fire or emergency. Keep the inside key where everyone can reach it quickly.
Three words that answer three different questions
Lock names get used loosely. People call any lock with a key a "deadlock", any surface lock a "Yale lock" and any lock inside the door a "mortice". That causes confusion when you're trying to describe a problem or buy a replacement. It helps to separate three questions:
- What holds the door shut? A sprung latch, a deadbolt, or both. This is where "deadlock" and "sashlock" come in.
- Where is the lock fitted? Screwed to the inside face of the door (a rim lock, which includes nightlatches) or set into a pocket in the door edge (a mortice lock).
- What does the key operate? Levers inside the lock case, or a separate cylinder.
So a single lock can be, for example, a "mortice sashlock with a euro cylinder": fitted into the door edge, with a latch and a deadbolt, worked by a cylinder key. Once you see the three questions separately, the names start to make sense.
Latch or deadbolt: what keeps the door closed
A latch is the bevelled tongue that springs out when the door closes and is pulled back by the handle. Its job is to stop the door blowing open. As Wikipedia's article on deadbolts puts it, a spring bolt is held in place by a spring, which is why it can't be relied on to keep anyone out.
A deadbolt is a square-ended bolt that moves only when you turn the key or thumbturn. Once it has been thrown into the frame, it can't simply be pushed back. A lock with only a deadbolt and no latch is a deadlock.
A sashlock combines both in one case: the handle works the latch for everyday use, and the key throws the deadbolt when you go out or go to bed. The name comes from the narrow glazed "sash" doors these locks were first made for.
A door that is only latched is closed, not locked. If your door shuts with a click and you never turn the key, the deadbolt isn't doing anything. That matters for insurance too: some home policies only cover theft where entry was forcible and violent, and insurers expect the locks you declared to be used.
Nightlatches: the lock on the face of the door
A nightlatch is a rim lock: a metal box screwed to the inside face of the door, with a matching keep screwed to the frame. A round rim cylinder passes through the door from the outside and drives the latch. Wikipedia notes that most rim locks on outside doors in Britain are nightlatches; you'll also see them on older South African homes and on flats, sometimes alongside a mortice lock lower down the door.
On a basic nightlatch, the latch springs shut when the door closes and is opened by the inside knob or the outside key. Many models have a small slide or button, called a snib, that holds the latch back so the door can be pushed open, or locks the knob. Deadlocking nightlatches go further: once the door is closed, the latch bolt locks in place so it can't be pushed back, and some let you lock the inside knob with the key. In the UK, nightlatches can be made to the BS 3621 standard, the same thief-resistance standard used for mortice locks there.
Because a nightlatch locks itself, people often rely on it alone. A plain, non-deadlocking nightlatch on its own is a convenience lock, not a security lock.
Mortice locks: the lock inside the door edge
A mortice lock sits in a rectangular pocket, the mortice, cut into the edge of the door. From outside you only see the faceplate on the door edge, the keyhole and the handles. "Mortice" only describes this way of fitting. As Wikipedia's article on mortise locks points out, it says nothing about the quality of the lock or its key mechanism.
Most South African front doors with a traditional key have a lever mortice lock, often sold as a "lockset" with handles. The key has a flag-shaped bit that lifts a set of levers inside the case. ASSA ABLOY's local Union range, for example, includes Gower locksets with two, three or four levers, listed as SABS approved, as well as a euro-profile version that takes a cylinder instead of levers.
Cutting the pocket removes timber from the door, so a mortice lock depends on a sound door edge and a properly fitted strike plate in the frame. A deep mortice in a thin or hollow door weakens it.
Seeing the difference on a real door
Quick checks you can do without removing anything:
- Is there a box on the inside face of the door? That's a rim lock, almost always a nightlatch on an outside door.
- Look at the door edge with the door open. A faceplate with a bevelled latch and a square bolt is a sashlock. A square bolt alone is a deadlock. A long faceplate running most of the door's height with several bolts or hooks is a multipoint lock.
- Look at the key. A key with a flag at the tip is a lever key. A flat key with cuts or dimples fits a cylinder.
- Read the faceplate. The maker's name and sometimes the model or standard are stamped on it. Take a photo.
Keyed on both sides: think about getting out
Many South African doors are locked with a key from both sides, especially where there's glass near the lock or a security gate in front of the door. That stops someone reaching through a broken pane to open it from inside. Wikipedia's article on deadbolts points out the trade-off: in a fire, people inside can't get out through a double-keyed door unless they can find the key.
The same tension shows up in standards. In the UK, BS 3621 covers locks keyed from both sides, while BS 8621 covers locks with a key outside and a handle or thumbturn inside, so people can leave without a key. Secured by Design describes BS 8621 as allowing keyless exit.
- If a door is keyed on both sides, keep the key in a fixed, known spot near the door (out of reach through any glass or burglar bars) whenever people are at home.
- Make sure everyone in the house, including children who are old enough and anyone who works there, knows where that key is.
- Where a thumbturn would be safer for the household, ask about it when the lock or cylinder is next replaced.
Repair or replace: what usually happens to each type
| Lock | Typical faults | Usually repairable? | When it's replaced |
|---|---|---|---|
| Nightlatch | Latch not catching the keep, worn rim cylinder, loose screws in a soft door | Often: keep adjustment, refixing, or a new rim cylinder | Case cracked or worn, or you want a deadlocking model |
| Lever sashlock or lockset | Stiff bolt, latch spring broken, handle drooping, worn key | Sometimes, if the fault is in the handles or strike rather than the case | Keys lost or compromised, levers worn, or the case has failed inside |
| Euro cylinder sashlock | Key stiff or won't turn, cylinder damaged | Often: the cylinder can be changed on its own | Case faulty, or upgrading to a higher grade lock |
| Mortice deadlock | Bolt rubbing on the strike, key hard to turn | Often, by adjusting the strike plate | Lost keys on a lever deadlock, or damage from forced entry |
If the key has gone missing, the lock type decides whether a single part can be changed: our guide on when to rekey and when to replace goes through it. For cylinder locks, it's worth reading about anti-snap cylinder upgrades before choosing a replacement.
- Don't spray general-purpose oil or grease into a lock. Lock makers give different advice on lubricants, so follow the maker's instructions or ask a locksmith.
- Don't open up a lever lock case. The levers and springs are small and easily reassembled in the wrong order.
- Don't force a key that won't turn. That's how keys snap off inside locks.
When a lock is past repair, we come out to you anywhere in Roodepoort for lock replacement or lock repairs. R250 call-out fee. The technician assesses the job on site and gives you the price before any work starts. Nothing is done until you agree. Send a photo of the door edge and the key on WhatsApp first and we'll tell you what we think it is. You can also start from our Roodepoort mobile locksmith page.
Questions
Is a "Yale lock" the same as a nightlatch?
In everyday speech, usually yes. Yale made the rim nightlatch famous, so the name stuck. But Yale also makes mortice locks, cylinders and digital locks, so if you're ordering parts, describe the lock rather than the brand: a box on the inside face of the door with a round cylinder outside.
Should I have a nightlatch and a mortice lock on the same door?
Two locks spread the load across the door and frame, and a nightlatch means the door is at least latched every time it closes. What matters most is using the deadbolt: a deadlock or sashlock that is never locked adds nothing.
Can a lever lock be swapped for a cylinder lock in the same hole?
Sometimes. The new lock case has to match the size of the existing pocket, the backset (the distance from the door edge to the keyhole) and the door thickness. If it doesn't, the door may need more work. A photo of the faceplate and a tape measure across the door edge help us check before the visit.
Need a locksmith to look at it?
If this hasn't solved the problem, our lock replacement service covers it. We're a mobile locksmith in Roodepoort, so we come to your door.
Sources and further reading
- Wikipedia: Mortise lock — Mortice describes a fitting method, not quality; sashlock and deadlock defined; lever and cylinder mortice locks; the mortice weakens a timber door
- Wikipedia: Rim lock — Rim locks attach to the surface of the door; most rim locks on British exterior doors are nightlatches
- Wikipedia: Deadbolt — Deadbolt versus spring bolt; double-cylinder deadbolts and the escape risk in a fire
- ASSA ABLOY South Africa: UNION locksets — Gower two-, three- and four-lever locksets and euro-profile lockset, listed as SABS approved
- Secured by Design: Locks and associated hardware standards — BS 3621 (key both sides), BS 8621 (keyless exit) and BS 10621 summarised
- Lockshop Warehouse: ERA 1830 BS 3621 high security nightlatch — Example of a UK nightlatch made to BS 3621, with automatic deadlocking, a snib and a lockable inside handle
- FAnews (Alexander Forbes Insurance): Does your home's security match your theft policy? — Insurers' minimum security requirements and theft cover limited to forcible and violent entry in some circumstances