A double cylinder deadbolt is a lock that needs a key to open from both inside and outside the door, unlike a standard single cylinder deadbolt, which only takes a key on the exterior. It adds strong protection against break-ins near windows, but it can slow down an emergency exit, which is why some Australian building codes restrict its use. Here’s how to weigh the pros and cons for your home.
What is a Double-Cylinder Deadbolt?
Before we get into the pros and cons, it helps to see how this lock actually works day to day. A double cylinder deadbolt is a lock that requires a key to unlock both the inside and outside of the door. Unlike a single cylinder deadbolt, which only requires a key on the exterior, a double cylinder deadbolt has a keyhole on both sides of the door.
These locks are commonly used in homes where extra security is needed, such as those with large windows near the doors. They offer a higher level of protection by making it harder for burglars to enter, especially if a window is broken and the intruder tries to reach in and unlock the door.
The Pros of Double-Cylinder Deadbolts
Enhanced Security
The most significant advantage of double cylinder deadbolts is their enhanced security. Since a key is required on both sides of the door, it’s much harder for a burglar to break into your home. If someone breaks a window near the door and tries to reach in, they won’t be able to unlock the door as they would with a single cylinder deadbolt. This added layer of protection makes forced entry much more difficult.
Ideal for High-Risk Areas
Double cylinder deadbolts are particularly useful in homes with entry doors near large windows. If a window is within arm’s reach of the door, a burglar could break the glass and unlock the door from the inside. Double cylinder deadbolts remove this vulnerability by requiring a key to open the lock, even from the inside. Pairing this with window locks on nearby glazing closes off that entry point completely, which matters most if you live in a high-crime area or your home is easily accessible from the outside.
Deterrent to Break-ins
No lock offers complete security, but double cylinder deadbolts are an effective deterrent. The added complexity of needing a key on both sides makes these locks less attractive to burglars looking for an easy target. They are more likely to move on to a home without this extra layer of security.
The Cons of Double-Cylinder Deadbolts
Fire Safety Concerns
The main drawback of double cylinder deadbolts is their impact on fire safety. In an emergency such as a fire, you may need to evacuate quickly. If a family member is trapped inside and the key isn’t within reach, it can delay the escape process. The extra security is great for preventing break-ins, but it’s a real risk in an emergency, which is part of good home security and burglary prevention planning overall. For this reason, some local building codes prohibit double cylinder deadbolts on doors with certain exit requirements.
Inconvenience
Another downside is needing a key on both sides of the door. If your hands are full with groceries or bags, digging out your keys to unlock the door from inside is a hassle. If you’ve misplaced your keys, getting back in becomes difficult. This is worth considering for homes with small children or elderly residents who may not always handle keys quickly.
Legal Restrictions
In some areas, double cylinder deadbolts are regulated by building codes or fire safety regulations, put in place to make sure occupants can exit quickly in an emergency. Because these locks can delay a quick exit, they may be restricted or prohibited on doors and windows that serve as primary exits. Check your local laws and regulations before installing one on your home.
Single Cylinder vs Double Cylinder Deadbolt
The two lock types solve different problems, and the table below shows where each one wins.
| Feature | Single cylinder deadbolt | Double cylinder deadbolt |
|---|---|---|
| Key needed outside | Yes | Yes |
| Key needed inside | No, uses a thumb turn | Yes, both sides need a key |
| Break-in resistance near windows | Lower, reachable through broken glass | Higher, glass access alone can’t unlock it |
| Fire and emergency exit safety | Higher, always exits without a key | Lower, may delay exit if key isn’t at hand |
| Common use case | Most residential exterior doors | Doors near large windows, high-security needs |
| Building code restrictions | Rarely restricted | Often restricted on primary exit doors |
This is also where a deadbolt vs deadlatch comparison matters if you’re deciding between lock families rather than just cylinder types. If your entry door doubles as your main emergency exit, a single cylinder deadbolt is the safer default. A double cylinder deadbolt earns its place on doors with glass panels or sidelights within arm’s reach of the lock, where the extra key requirement closes off the most common break-in method.
When to Choose a Double-Cylinder Deadbolt
Given the pros and cons above, here are the situations where a double cylinder deadbolt is the right fit.
High-Security Needs
If you live in a high-crime area or have concerns about break-ins, double cylinder deadbolts provide that extra layer of security. They’re ideal for homes with large windows near the door or areas where burglars could easily break in and reach for the lock.
Protecting Vulnerable Areas
If you have entry doors near a large window or other potential entry points, a double cylinder deadbolt is a valuable addition to your home security. It stops burglars from using a broken window to unlock your door and gain access.
When You Don’t Mind the Inconvenience
If you’re comfortable needing a key on both sides of the door, and fire safety isn’t a concern because the lock isn’t on a primary exit, a double cylinder deadbolt can be a good option. If ease of access matters more to you or your family, look at other lock types instead.
Frequently Asked Questions
Are double cylinder deadbolts legal?
It depends on your location and the door’s fire exit status. Many Australian fire safety codes restrict or prohibit double cylinder deadbolts on doors that serve as a primary emergency exit, because the inside key can delay evacuation. Check with your local council or a licensed locksmith before installing one on an exit door.
What is the difference between a single and double cylinder deadbolt?
A single cylinder deadbolt uses a key outside and a thumb turn inside, so you can always exit without a key. A double cylinder deadbolt requires a key on both sides, which blocks intruders from reaching through a broken window to unlock the door, but also blocks a quick exit from inside.
Is a double cylinder deadbolt worth it for home security?
It’s worth it for doors near large windows or in high-crime areas, where the added key requirement stops a break-in through glass. It’s generally not worth the fire safety trade-off on a door that’s your main way out in an emergency.
Can I install a double cylinder deadbolt myself?
You can, but get the door’s exit status checked by a licensed locksmith first. Getting this wrong on an exit door can breach local fire codes and create a real safety risk for your household.
Are Double-Cylinder Deadbolts Right for You?
Double cylinder deadbolts are a strong security option for some homes, but not for everyone. They offer enhanced protection, especially where windows sit close to the door, but they come with real trade-offs: fire safety concerns and the inconvenience of needing a key on both sides.
If you’re unsure whether a double cylinder deadbolt is right for your home, or want to discuss other security options, reach out to us at Ambassador Locksmiths. Our licensed locksmiths can assess your doors and windows, recommend the right lock setup for your household, and carry out the installation or upgrade for you.
Your security is our priority, and we’re here to help you keep your home safe.