Yes — installing a chain lock or door guard is one of the more approachable home security DIY jobs. Neither task involves restricted trade work, so as a homeowner you're free to do it yourself. That said, doing it properly matters: a poorly fixed chain lock can be ripped off a door frame with a single firm kick, giving a false sense of security rather than real protection.
What's the Difference Between a Chain Lock and a Door Guard?
Chain locks (also called door chains) use a short metal chain attached to the door frame, with a sliding fitting on the door itself. They let you open the door a crack to speak with a caller without fully unlocking it.
Door guards (sometimes called door limiters or door bars) work on a similar principle but use a rigid bar or reinforced arm instead of a chain. They're generally stronger and harder to force than a basic chain lock.
Both are supplementary security devices — they work alongside your main deadbolt or latch, not instead of it.
Tools and Materials You'll Need
- Cordless drill and drill bits (wood and, if needed, masonry bits)
- Screwdriver (usually Phillips head)
- Pencil and tape measure
- Spirit level
- Appropriate screws and, ideally, long security screws (75–100 mm) to reach the door frame stud
- Wall plugs if fixing into a hollow or masonry surface
- The chain lock or door guard kit (most come with screws, though these are often too short — upgrade them)
You'll find a good range of door chains and guards at Bunnings and Mitre 10. Look for solid brass or stainless steel fittings rather than lightweight zinc alloy, which can fail under pressure.
Step-by-Step Installation Guide
1. Choose the Right Height
Fit the chain or guard at a comfortable height for adults in your household — typically between 1,400 mm and 1,600 mm from the floor. Make sure it's out of reach of young children if that's a concern.
2. Mark the Positions
Hold the door-side fitting against the door edge (the face of the door, not the jamb) and mark the screw holes with a pencil. Do the same for the frame-side fitting on the door frame (jamb). Use a spirit level to keep everything aligned.
3. Pre-Drill Your Holes
Pre-drill pilot holes slightly smaller than your screw diameter. This prevents the timber from splitting, especially on older NZ homes with dry or painted timber frames.
4. Use Long Screws — This Is Critical
The screws supplied in most budget kits are often only 25–30 mm long. These may only grip the door stop or the thin jamb casing, not the structural framing behind it. Replace them with 75–100 mm screws that reach into the solid framing stud behind the jamb. This dramatically increases resistance to forced entry.
5. Fit the Door-Side Component First
Screw the chain bracket or guard arm fitting to the door itself. Most interior doors in NZ are solid-core or hollow-core — if hollow-core, try to position fixings near the door edge where there's more solid timber.
6. Fit the Frame-Side Component
With the door closed, position the frame plate so the chain or arm engages smoothly when the door is opened slightly. Mark, pre-drill, and screw into place using your long screws.
7. Test It
Open and close the door several times to check the chain or guard engages and releases easily. Make sure the door can open the intended amount — typically 60–100 mm for a chain lock.
NZ Building Code and Rental Considerations
Fitting a chain lock or door guard is generally exempt from building consent under Schedule 1 of the Building Act 2004, as it's minor maintenance and repair work. However, if you're making changes to a fire-rated door or a door in a multi-unit dwelling, check with your local council first — requirements can vary. See MBIE Building Performance for guidance on what requires consent.
If you're a landlord, note that the Healthy Homes Standards set minimum requirements for rental property security, including that all exterior doors must have working locks. A chain lock alone won't satisfy the main lock requirement, but it can be a useful addition.
If you're a tenant, check your tenancy agreement before drilling into doors or frames — you may need your landlord's written permission for any modifications.
When to Call a Professional
While chain locks and door guards are DIY-friendly, consider calling a qualified locksmith if:
- Your door frame is damaged, rotten, or misaligned — fixings won't hold properly and the frame may need repair first
- You want to upgrade to a high-security door limiter with reinforced strike plates, which may require more complex installation
- You're unsure about the construction of your door (e.g., aluminium-framed doors, sliding doors, or fire doors need specialist advice)
- You're fitting security hardware after a break-in and want a professional security assessment
- You're a landlord wanting to ensure compliance with tenancy legislation
A qualified locksmith can also advise on whether your existing deadbolt and door frame are strong enough — a chain lock on a weak door is only as good as the door itself. You can find a trusted local locksmith on tradedirectory.co.nz.
