How to change a door lock in Sydney (and the 4 times you must call a locksmith)

It's 7 AM on a Saturday. You've just collected the keys from your conveyancer for a three-bed semi in Marrickville, and the vendor cheerfully handed over a single, badly copied key. You're standing at the front door wondering if you can just buy a new deadbolt from Bunnings and sort this yourself before lunch.

By the end of this guide, you'll know exactly how to change a door lock, when it's a 20-minute DIY job, and the four specific scenarios where you need to stop, put the drill down, and call a licensed locksmith.

The tools you need (and the one nobody mentions)

Changing a standard residential deadbolt requires a remarkably short list of gear. You likely have most of it in the junk drawer.

• A Phillips head screwdriver (a No. 2 fits 90% of residential screws)
• A flathead screwdriver for prying off faceplates
• A tape measure
• A replacement deadbolt kit (more on choosing the right one below)

The tool nobody mentions: a small magnet. Drop the mounting screws on a tiled entry porch and they vanish into the grout lines. A magnet saves you twenty minutes of crawling around.

How to change a door lock: the basic DIY process

If you have a standard wooden door and you're replacing a deadbolt with another deadbolt of the same backset (the distance from the edge of the door to the centre of the hole, usually 60mm in Australia), this is a simple swap.

Remove the two screws on the inside faceplate. Pull the inside cylinder out, then push the outside cylinder through the door. Unscrew the two screws holding the latch bolt on the edge of the door, and slide the old latch out.

Slide the new latch in. Ensure the word "UP" on the latch faces the top of the door. Secure it with the two screws on the edge. Push the outside half of the new cylinder through the door, align the tailpieces with the latch mechanism, and secure the inside cylinder with the two long mounting screws.

Test it with the door open. Then test it with the door closed.

Done.

This whole process should take about 15 minutes if the holes line up.

Rekey vs replace locks: which makes sense?

When you move into a new place, you have two options: replace the hardware entirely or rekey the existing cylinders. Rekeying means a locksmith adjusts the internal pins of the existing lock so old keys no longer work.

If your hardware is relatively new, high-quality, and functions smoothly, rekeying is almost always the better choice. It costs less — usually around $80 to $120 per cylinder if you pay a mobile locksmith, though honestly nobody quotes this consistently — and it keeps solid hardware out of landfill.

If you're holding a $30 bargain-bin deadbolt, replace it. The price difference to rekey cheap hardware isn't worth it, and the security on those units is marginal at best. A decent single-cylinder deadbolt from a reputable brand will set you back about $90 to $140 at a hardware store.

The Wenest take

In the homes we work in across Sydney's inner west, the version of this that actually goes wrong isn't the lock itself. It's the strike plate. People swap the deadbolt, test it with the door shut, and it latches fine. But they didn't check the strike plate — the metal recess in the door frame. The bolt extends, but it's only catching the edge of the plate, not sitting fully inside the recess. One decent shoulder-check and the door opens. We see this constantly in Federation homes where the timber frames have shifted over decades. The fix is simple: move the strike plate 3mm down and use longer 75mm screws that bite into the wall framing, not just the door jamb.

When to call a locksmith: the 4 hard stops

DIY is fine for a straight swap on a wooden door. But there are four scenarios where you need to stop and call a professional.

1. You've lost track of who has keys

A client in Randwick bought a post-war brick duplex last February. The selling agent mentioned, almost as an afterthought, that the previous tenant had been there for nine years and "probably had a few copies made". The new owners found out later the old housemate still had a key and was using the laundry when they weren't home.

If you don't have a complete chain of custody for every key, you need a full rekey or lock replacement across every entry point. Do the back door and the garage, not just the front.

2. The door is metal or aluminium

Metal doors require a specialised hole saw and a centre punch. If your cross-bore (the main hole through the door) doesn't match the new lock, drilling through a metal fire door is a fantastic way to ruin a $400 piece of hardware and create a sharp, jagged edge that will slice your hand open. Call someone who does this every day.

3. You want a master key system

If you want one key to open the front, back, garage, and the side gate, you need a master key system. This is not a DIY job. It requires specific pin tumbler configurations that are mathematically complex to set up. A botched master system will jam constantly and leave your doors vulnerable to bump keys.

4. You suspect the frame is compromised

If the door frame shows signs of previous forced entry, rot, or warping, a new lock won't fix the underlying structural weakness. You need a locksmith to assess the frame, install a reinforced strike box, and potentially fit a longer deadbolt. This is core home security, not a weekend project.

Upgrading your deadbolt in Sydney

If you're upgrading, avoid smart locks that rely entirely on a touchscreen with no manual key override. When the battery dies — and it will, usually on a rainy Tuesday when you're carrying groceries — you are locked out.

Look for a deadbolt with a keyway on the outside and a thumb-turn on the inside. If you want smart features, choose a hybrid that lets you use a physical key as a backup. We generally recommend sticking to established mechanical brands unless you're willing to commit to changing batteries every eight months without fail.

For strata properties, check your by-laws before changing any external door hardware. Some buildings mandate specific finishes or lock types to maintain a uniform streetscape. NSW Fair Trading has guidelines on alterations in strata schemes if you're unsure where your building sits.

Scheduling a home security inspection

A lock replacement is often the trigger for a broader look at your home's security. A home security inspection covers door frames, window locks, sensor light placement, and garage entry points.

If you've just moved in, this is worth doing once. A licensed locksmith can walk the property in 45 minutes and give you a prioritised list of weak points. You don't have to fix everything in week one, but knowing where the vulnerabilities are lets you plan.

We coordinate this exact kind of assessment for our members in Sydney. If you've just settled on a property and don't want to play project manager with three different tradespeople to secure the house, see how Wenest works or become a member.

This article is general guidance only. Any structural modifications to security doors or frames should be assessed by a licensed tradesperson — see NSW Fair Trading for licence verification.