The Complete Guide to Door Locks and Deadbolts — The First Line of Defence for Your Home

Why Your Door Lock Matters More Than You Think

A door lock serves three purposes. First, it physically prevents the door from being opened by an unauthorised person. Second, it deters opportunistic intruders — visible, quality locks signal that the property is protected, encouraging the opportunist to move on. Third, it satisfies insurance requirements — most home insurance policies stipulate minimum lock standards on external doors, and a claim may be refused if the locks do not meet the specified standard at the time of a break-in.

The vast majority of domestic burglaries are opportunistic — the intruder looks for the easiest point of entry and moves on if the resistance is too great. A quality lock, properly fitted, provides exactly that resistance. It does not need to be impregnable — it needs to be sufficiently difficult to defeat that the opportunist chooses an easier target.

Deadbolts — The Essential Front Door Lock

A deadbolt is a locking bolt that is extended into the door frame by turning a key or thumb turn. Unlike a spring latch (which can be pushed back), a deadbolt must be actively unlocked — it cannot be forced back by pushing, prying, or credit-card shimming. This makes it fundamentally more secure than a latch alone.

Single-cylinder deadbolts have a key on the outside and a thumb turn on the inside. They are the standard for most residential front doors — secure from outside, easily opened from inside in an emergency.

Double-cylinder deadbolts require a key on both sides. They provide additional security on doors with glass panels (an intruder cannot break the glass and reach inside to turn a thumb turn), but they present a safety concern — in an emergency, the occupant must locate a key to exit. Some jurisdictions restrict or regulate double-cylinder deadbolts for this reason.

The bolt throw (how far the bolt extends into the frame) affects security. A longer bolt throw is harder to pry or force. A minimum of 20 mm (3/4 inch) is standard; higher-security deadbolts offer 25 mm (1 inch) or more.

Deadbolt grade ratings (where applicable in your region) indicate the lock's resistance to forced entry, drilling, and picking. The highest-grade deadbolts resist kick-ins, drilling, and picking significantly better than budget alternatives.

Mortice Locks — The Traditional Timber Door Standard

A mortice lock is fitted within the body of the door (morticed into the edge) rather than mounted on the surface. This makes it inherently more resistant to physical attack than a surface-mounted lock — the lock mechanism is protected by the door's timber.

Five-lever mortice deadlocks are the traditional standard for securing external timber doors. The term "five-lever" refers to the internal mechanism — five separate levers must be lifted to the correct height by the key before the bolt can be thrown. More levers mean more possible key combinations and greater resistance to picking.

Mortice sash locks combine a deadbolt with a spring latch in a single unit. The latch holds the door closed when unlocked (operated by a handle), while the deadbolt provides security when locked (operated by a key). They are the most common lock type for residential front doors on timber frames.

Security-rated mortice locks that conform to recognised standards (such as the British Standard BS 3621 or equivalent in your region) include hardened steel components that resist drilling, sawing, and picking. Insurance companies typically require locks meeting these standards on external doors.

Cylinder Locks — Euro Profile and Rim Cylinders

A cylinder lock uses a removable cylinder that contains the pin mechanism — the part the key operates. The cylinder slots into a lock body (either a mortice lock body or a multi-point lock) and can be replaced independently if the keys are lost or the cylinder is damaged.

Euro profile cylinders are the most common cylinder type, used in the majority of modern uPVC, composite, and aluminium doors with multi-point locking systems. They are barrel-shaped and slot into the lock body from the edge of the door.

The cylinder snapping vulnerability

Standard euro profile cylinders have a well-documented vulnerability: they can be snapped. An intruder grips the protruding section of the cylinder (the part visible on the outside of the door), applies force (using pliers, a wrench, or even by hand on poorly fitting cylinders), and snaps the cylinder at its weakest point. Once snapped, the remaining mechanism can be manipulated to open the lock.

Anti-snap cylinders are specifically designed to resist this attack. They incorporate a sacrificial snap line — a controlled weak point that, if snapped, breaks away the outer section while leaving the core mechanism intact and secure. The lock remains locked even after the snap attack.

When purchasing a euro profile cylinder, always choose an anti-snap model. Standard cylinders without anti-snap protection are a known security weakness that is actively exploited. The additional cost of an anti-snap cylinder over a standard one is trivial compared to the security improvement.

Additional cylinder security features include anti-pick (internal mechanisms that resist lock-picking tools), anti-drill (hardened pins that break drill bits), and anti-bump (resistance to the bumping technique that opens standard pin-tumbler cylinders using a specially cut key).

Rim cylinders are used with night latches and some surface-mounted locks. They mount on the inside surface of the door with the key-operated cylinder passing through to the outside.

Multi-Point Locking Systems — Modern Door Security

Multi-point locks engage bolts or hooks at multiple points along the height of the door — typically three, five, or even seven locking points — rather than at a single position. This distributes the locking force across the full height of the door, making it significantly more resistant to forced entry than a single lock.

Multi-point locks are standard on uPVC and composite doors. They are operated by a single turn of the key in the euro profile cylinder, which engages all locking points simultaneously.

The security of a multi-point lock depends on the cylinder. The lock body may be strong, but if the euro profile cylinder is a standard (non-anti-snap) model, the entire system can be defeated by snapping the cylinder. Upgrading the cylinder to an anti-snap, anti-pick, anti-drill model secures the entire multi-point system.

Night Latches — Convenience With Limitations

A night latch (also called a Yale-type latch or deadlatch) is a surface-mounted lock that latches automatically when the door is closed. It provides convenient everyday access — you pull the door closed behind you and it locks automatically — and is opened from inside by a handle or knob.

Night latches do not provide high security on their own. The spring-loaded latch can potentially be defeated by manipulation, and the surface-mounted case can be attacked more easily than a mortice lock embedded within the door. Insurance companies typically do not accept a night latch as the sole lock on an external door.

A night latch should always be paired with a deadlock (either a mortice deadlock or a deadbolt) on external doors. The night latch provides everyday convenience; the deadlock provides the actual security. When leaving the house or at night, engage the deadlock in addition to the night latch.

Deadlocking night latches include a mechanism that prevents the latch from being pushed back when the door is closed, providing improved security over basic spring latches. Look for this feature on any night latch fitted to an external door.

Internal Door Locks — Privacy and Function

Internal doors require locks for privacy (bathrooms, bedrooms) rather than security. The requirements are different from external doors.

Privacy locks (bathroom locks) include a thumb turn on the inside for locking and an emergency release on the outside (a small slot that can be turned with a coin or flat-blade screwdriver) to allow access in an emergency. They do not require a key.

Passage latches hold the door closed but do not lock. They are used for rooms that do not require privacy — living rooms, kitchens, and hallways. A handle operates the latch; there is no locking mechanism.

Tubular latches are the standard mechanism for internal doors — a spring-loaded bolt that retracts when the handle is operated and extends again to hold the door in the closed position.

Security Standards and Ratings — What to Look For

Different regions have different lock security standards. The specific standard varies, but the principle is universal: a tested, certified lock provides documented resistance to specific attack methods, while an untested lock provides no such assurance.

Look for locks that display a recognised security certification mark relevant to your region. These certifications indicate that the lock has been independently tested against defined criteria for resistance to forced entry, drilling, picking, and other attack methods.

Insurance requirements typically specify a minimum lock standard for external doors. Check your home insurance policy for specific requirements — a claim for burglary may be refused if your locks do not meet the stipulated standard. If in doubt, contact your insurer to confirm what lock specification is required.

Higher-security locks cost more — but the difference is typically modest compared to the value of the security improvement. A certified, high-security deadlock for an external door costs only marginally more than a budget alternative but provides dramatically better protection and satisfies insurance requirements.

Lock Cylinders — The Vulnerable Component

The cylinder is the most frequently attacked component of a lock system. Upgrading the cylinder is often the most effective and economical security improvement you can make — particularly on doors with multi-point locks where the lock body itself is adequate but the cylinder is the weak point.

When purchasing a replacement cylinder, measure the existing cylinder precisely. Euro profile cylinders are measured by their total length and the split between the internal and external sides. A cylinder that is too long protrudes from the door and is easier to attack. A cylinder that sits flush with the door face (or is slightly recessed behind a protective escutcheon) is more secure.

Cylinder security ratings (where applicable in your region) provide a clear indication of the cylinder's resistance to snapping, picking, drilling, and bumping. The highest-rated cylinders resist all common attack methods.

Door Reinforcement — Strengthening the Whole System

A lock is only as strong as the door and frame it is fitted to. A high-security lock in a weak door frame can still be kicked in — the frame splinters and the lock, still engaged, comes away with it.

Reinforced strike plates replace the standard thin metal plate in the frame where the bolt engages. A heavy-duty strike plate with long screws (75 to 100 mm / 3 to 4 inches, reaching into the structural frame rather than just the door lining) dramatically increases resistance to kick-in attacks.

Door wrap-around plates reinforce the area of the door around the lock, preventing the door from splitting at the lock bore under forced entry.

Hinge bolts (dog bolts) are metal pins fitted to the hinge side of the door that engage with holes in the frame when the door is closed. Even if the hinges are removed or fail, the hinge bolts prevent the door from being lifted away. They are particularly important for outward-opening doors where the hinge pins are accessible from outside.

A security chain or door limiter allows the door to be opened a few centimetres while remaining secured — useful for verifying a visitor's identity before fully opening the door. A chain alone does not provide high security (chains can be cut), but it provides a useful additional barrier.

Lock Comparison Table

Common Mistakes People Make

Relying on a night latch as the only lock on an external door

A night latch alone does not provide adequate security for an external door. It should always be paired with a deadlock or deadbolt. Always engage the deadlock when leaving the house and at night.

Using a standard euro cylinder on a uPVC or composite door

Standard euro cylinders are vulnerable to snapping — a well-known attack method that takes seconds. Replacing a standard cylinder with an anti-snap, anti-pick, anti-drill model is one of the most impactful and affordable security upgrades you can make.

Not checking insurance lock requirements

Many home insurance policies require specific lock standards on external doors. If your locks do not meet these requirements, a burglary claim may be refused. Check your policy and upgrade if necessary.

Fitting a high-security lock in a weak frame

A lock can only resist as much force as the frame it is fitted to. A reinforced strike plate with long screws that reach into the structural framing (not just the door lining) dramatically improves kick-in resistance. This is a simple, inexpensive upgrade that significantly strengthens the entire door system.

Leaving a cylinder protruding from the door face

A euro cylinder that protrudes beyond the door face or the escutcheon plate is easier to grip and snap. The cylinder should sit flush with or slightly behind the door surface. Measure precisely when purchasing a replacement and choose the correct length.

Forgetting the hinge side

Security focus tends to concentrate on the lock side of the door, but the hinge side is equally vulnerable on outward-opening doors. Hinge bolts prevent the door from being removed even if the hinges are compromised.

The Honest Limitations

No lock is impregnable. Given enough time, tools, and determination, any lock can be defeated. The purpose of a domestic lock is to resist attack for long enough to deter opportunistic intruders and to provide sufficient evidence of forced entry for insurance purposes. A lock that resists attack for several minutes is highly effective — most opportunistic burglars will move on within seconds if the lock does not yield quickly.

A lock protects the door — not the window, the garage, or the patio. A high-security front door lock is of limited value if other entry points (windows, back doors, garage doors) are weakly secured. Security should be considered holistically across all entry points.

Lock quality varies enormously within the same price range. Two locks at the same price point can differ dramatically in security performance. Look for certified locks with documented test results rather than relying on price as an indicator of quality.

Professional fitting matters. A high-security lock that is poorly fitted — misaligned, inadequately supported, or incorrectly installed — underperforms. For external door locks, particularly mortice locks and multi-point systems, professional fitting by a locksmith ensures the lock performs to its designed specification.

Pre-Purchase Checklist

What type of door do you have?

Timber door: mortice deadlock or mortice sash lock (certified to your regional standard). uPVC or composite door: upgrade the euro profile cylinder to an anti-snap, anti-pick, anti-drill model. Any door: add or upgrade a deadbolt.

Does your current lock meet your insurance requirements?

Check your policy. Upgrade if necessary.

Is the door frame reinforced?

Install a heavy-duty strike plate with long screws. Add hinge bolts on outward-opening doors.

Do you need convenience features?

If keyless entry or remote access is desired, see our separate guide to smart locks.

Have you measured the cylinder correctly?

For euro profile cylinder replacement, measure the existing cylinder's total length and the internal/external split precisely. A cylinder that is the wrong length compromises both security and function.

Why Buying Through Amazon Is a Smart Option

Amazon carries door locks and deadbolts from every major manufacturer — mortice locks, euro cylinders, deadbolts, night latches, and reinforcement hardware — alongside fitting tools and accessories. Customer feedback provides practical insight into security performance, fitting quality, and real-world durability. Free returns on most purchases allow you to check dimensions and compatibility before final fitting.