Deadlocks & Door Security Explained

A deadlock is one of the most important locks on a timber door, and it is often the lock your insurer asks about. The confusing part is that "deadlock" can mean several different things. This guide explains the main types, where each belongs, and how to think about door security without overcomplicating it.

What a deadlock actually is

A deadlock throws a solid bolt into the door frame and can only be moved with a key. There is no handle or sprung latch involved. That simplicity is the point: the door relies on a solid bolt rather than a latch that can be slipped.

Because the key is needed from both sides, a burglar cannot simply reach through a letterbox or broken nearby glass to open the lock, as long as the key is removed from the inside.

The main deadlock types

1. Mortice deadlock for timber doors

A mortice deadlock is fitted inside the edge of a wooden door, so only the faceplate and keyhole show. It is key-only, with no handle. This is the classic strong option for front and back timber doors.

• Standard 2 or 3 lever locks: usually for internal doors, sheds, and outbuildings. They are not the right choice for external final exit doors.
• 5 lever BS3621 locks: the version most insurers expect on timber exit doors. Look for the BSI Kitemark and BS3621 on the faceplate.

2. Mortice sashlock for doors with handles

A sashlock uses the same mortice style fitting, but it combines a deadbolt with a sprung latch. That means the door can work with handles day-to-day, then lock securely with a key. For external timber doors, look for BS3621 versions.

3. Euro-profile deadlock for timber and aluminium doors

A euro-profile deadlock is a mortice deadlock case operated by a removable euro cylinder. It can be useful because the cylinder can be replaced or upgraded separately, but the cylinder then needs its own security rating, such as TS007 3-star or SS312.

4. Rim deadlock or deadlocking nightlatch

A rim lock is fitted on the surface of the door, often above a mortice lock. A basic rim nightlatch can be convenient, but it offers limited security by itself. A British Standard deadlocking nightlatch is stronger, but on a wooden front door it is normally paired with a mortice deadlock.

Deadlock vs sashlock: the quick answer

• Deadlock: key only, no handle, just a solid bolt. Often used as the secure second lock on a door.
• Sashlock: deadbolt plus a latch for handles, so it is the everyday operating lock and the secure lock in one.
• Layered security: many timber doors use both a deadlock and a nightlatch.

Standard vs British Standard and insurance

A non-British-Standard deadlock can look similar to a certified lock, but it may not meet what most policies require on exit doors. A BS3621 5 lever deadlock is independently tested against common attack methods such as drilling, picking, and force.

Many UK home policies make a BS3621 lock on final exit doors a condition of cover. That does not mean every property is the same, so always check your own policy wording. If you are unsure, send a photo of the lock faceplate and we can explain what the markings mean.

Deadlocks as part of overall door security

A deadlock is one layer. A strong door setup usually combines the right lock, the right cylinder, a sound frame, suitable hinges, and sensible habits. For example, a strong lock in a weak frame will not perform as well as it should.

• Use the right deadlock for the door type.
• Choose BS3621 on timber final exit doors where your policy requires it.
• Use anti-snap 3-star cylinders where euro cylinders are fitted.
• Remove keys from the inside when the door is locked.
• Ask for proportionate advice rather than unnecessary upgrades.

Useful links

Lock changes in Finsbury Park uPVC door and window repairs Burglary repairs

Deadlock FAQs