Deadlocks Explained: Types, Australian Standards, and Why They Matter for Your Melbourne Home
If you've ever asked a locksmith what the single most important security upgrade for a Melbourne home is, the answer is almost always the same: a quality deadlock on every external door. It's a recommendation that comes up consistently, across property types, suburbs, and budgets — and for good reason.
Yet despite being the foundation of residential security, deadlocks are widely misunderstood. Many homeowners aren't sure what distinguishes a deadlock from a standard door lock, what the different types offer, or what the Australian Standard rating on the packaging actually means for their security. These are important things to understand, because not all deadlocks provide the same level of protection — and choosing the wrong one can create a false sense of security that a determined intruder can exploit.
At
Malvern Lock Service, we install, repair, and assess deadlocks across Malvern, Toorak, Hawthorn, Armadale, Camberwell, and Melbourne's inner south suburbs every day. This guide explains what deadlocks are, how the main types differ, what Australian Standard AS4145 means in practice, and why getting the specification right matters for your home.
What Is a Deadlock?
A deadlock is a locking mechanism in which the bolt — the physical piece that extends from the lock into the door frame — can only be moved by turning a key or thumb turn. Unlike a spring latch, which retracts automatically when the door handle is pressed, a deadlock bolt does not retract unless deliberately operated.
This distinction matters because spring latches can often be manipulated using a credit card, thin tool, or similar object slipped between the door and frame. A deadlock bolt, by contrast, is solid, square-ended, and cannot be pushed back without the correct key. This makes deadlocks significantly more resistant to common forced entry techniques.
Deadlocks provide protection against:
Credit card or shimming attacks on spring latches
Bump key attacks, when a high-quality cylinder is used
Lock picking, particularly with higher-grade cylinders
Forced pushing or pulling of the door when correctly installed with a quality strike plate
The Main Types of Deadlocks
Deadlocks come in several configurations, each suited to different door types, property styles, and security requirements. Understanding the differences helps in selecting the right option for each entry point on your property.
This creates real risks in several common situations:
Single Cylinder Deadlock
The most common type found in Melbourne homes. A keyed cylinder on the exterior allows entry from outside, while a thumb turn on the interior allows exit without a key.
Single cylinder deadlocks are practical for most residential entry points. They allow quick exit in an emergency without needing to locate a key, while maintaining keyed security from the outside.
Double Cylinder Deadlock
Requires a key to operate from both the inside and outside. There is no thumb turn — a key is needed to lock and unlock the door from either side.
Double cylinder deadlocks are sometimes used on doors with glass panels nearby, where a thumb turn could be reached and operated by someone who has broken the glass. However, they raise important safety considerations around emergency exit and are not suitable for all situations. A licensed locksmith can advise whether a double cylinder is appropriate for your specific door and layout.
Mortice Deadlock
A mortice lock is fitted inside the body of the door itself rather than on the surface. The lock case is recessed into a cavity cut into the door edge, making it significantly more tamper-resistant than surface-mounted options.
Mortice deadlocks are commonly found in older Melbourne properties, particularly those with solid timber doors in heritage suburbs like Armadale, Hawthorn, and Malvern. They are robust and well suited to doors with sufficient timber depth to accommodate the lock case.
Rim Deadlock
A surface-mounted lock attached to the inside face of the door, with a bolt that engages a strike plate on the door frame. Rim deadlocks are often used as a secondary lock on doors that already have a primary lock, or on doors where mortice installation is not practical.
They are a common sight on older properties and can provide a useful additional layer of security when a mortice or cylinder deadlock is already in place.
These are not hypothetical scenarios. They represent some of the most common reasons homeowners across suburbs like South Yarra, St Kilda, and Prahran contact us to have their locks re-keyed or changed — because they can no longer be certain who holds a working copy of their key.
Australian Standard AS4145: What It Means and Why It Matters
When shopping for deadlocks in Australia, you will frequently encounter references to AS4145 — the Australian Standard for mechanical lock sets. Understanding what this standard measures helps you evaluate whether a lock will actually perform when it needs to.
AS4145 grades locks across several performance categories based on independent testing. The standard assesses resistance to a range of attack methods and assigns grades accordingly.
The key performance areas tested under AS4145 include:
Cylinder security — resistance to picking, drilling, and pulling attacks on the lock cylinder
Bolt strength — resistance to forced retraction, sawing, and cutting of the bolt itself
Overall lock body strength — resistance to the lock being torn away from the door under force
Key control — the difficulty of duplicating the key without authorisation
What the grades mean in practice:
Grade 1 — minimum performance, suitable for low-security applications
Grade 2 — moderate security, appropriate for general residential use
Grade 3 — high security, recommended for properties requiring stronger protection
Grade 4 and above — maximum security, typically specified for commercial or high-risk applications
For most Melbourne homes, a Grade 2 or Grade 3 rated deadlock provides appropriate security. The specific grade required depends on the property type, location, and any relevant insurance requirements.
Why the AS4145 rating matters:
Locks without an AS4145 rating have not been independently tested and cannot be verified to meet any defined security standard
A lock that looks substantial but carries no rating may use a low-grade cylinder that can be picked or drilled in seconds
Insurance policies for Melbourne properties sometimes specify minimum lock standards — checking your policy before selecting a lock avoids the risk of a claim being denied due to inadequate hardware
The Cylinder Is the Most Critical Component
Many homeowners focus on the visible elements of a deadlock — the body, the finish, the handle — while underestimating the importance of the cylinder. The cylinder is the component that accepts the key and controls access. It is also the component most frequently targeted by intruders.
A quality cylinder should:
Carry a rating that meets or exceeds AS4145 requirements at the appropriate grade
Include anti-pick, anti-drill, and anti-bump features, which are standard on higher-grade cylinders
Use a restricted key profile if key control is a priority, preventing unauthorised duplication
At Malvern Lock Service, cylinder quality is assessed as part of every lock installation and repair recommendation. A deadlock body rated to Grade 3 is significantly undermined by a low-grade cylinder — and this mismatch is more common in off-the-shelf products than most homeowners realise.
Installation Quality Is Just as Important as Lock Quality
Even the highest-rated deadlock will underperform if it is incorrectly installed. The most common installation failures that reduce deadlock effectiveness include poorly fitted strike plates, inadequate fixing screws, and misaligned bolt throws that prevent the bolt from fully engaging the frame.
Correct installation requires:
A strike plate with sufficient depth and fixing length to resist kick-in attacks
The bolt throw fully extending into the door frame — not just catching the surface
Correct alignment so the bolt engages cleanly without forcing or binding
Fixing screws of adequate length to reach the structural timber behind the frame
Professional installation by a licensed locksmith ensures that the deadlock performs to its rated specification. A correctly installed Grade 2 deadlock provides considerably more real-world security than a Grade 3 lock fitted poorly.
Conclusion
Deadlocks are the foundation of residential security for good reason — when correctly specified and installed, they provide reliable, long-term protection against the most common forced entry methods. Understanding the different types, what the AS4145 rating actually measures, and why cylinder and installation quality matter puts you in a far better position to make the right choice for your property.
If you are in Malvern, Toorak, Hawthorn, Armadale, Camberwell, or anywhere across Melbourne's inner south suburbs and want honest advice on deadlock selection, installation, or an assessment of your current locks,
Malvern Lock Service is ready to help. Our team will assess your specific doors, frames, and security requirements and recommend the most appropriate solution — with no unnecessary upgrades.