Can You Add a Key Lock to a Sliding Door?
And Why It Takes Two Visits

A lot of sliding doors in Auckland lock from the inside and nowhere else. You pull the door shut, flick the catch, and that is it — there is no key, so there is no locking it behind you on the way out. Which is fine until that is the door you actually use.

First, Look for the Blind Plug

Most sliding door handles are made in two versions of the same body: one with a key barrel, one without. On the one without, the hole where the barrel would sit is filled with a plain cap — a blind plug. If you can see that cap on your handle, you are looking at the non-keyed twin of a lock that definitely exists in a keyed version.

Here is the thing people try first and should not: you cannot pop that cap out and push a barrel in. The keyed version is a different internal mechanism, not the same lock with an extra hole. The fix is swapping the whole unit.

Why a Tape Measure Will Not Settle It

Sliding door locks are not a standard part. Four things have to line up on the replacement, and every one of them varies by door brand and by age:

• The mortise — the depth and height of the slot cut into the door edge
• The fixing centres — where the screws land
• The backset — how far the barrel sits back from the edge
• The keeper — the plate already set into the jamb that the bolt throws into

Sliding door hardware is full of near-misses: parts that are three millimetres out, or have the screws in a slightly different place. A near-miss means fresh holes, packed-out gaps and a door that looks repaired. The door was fine before — it should still look fine afterwards.

So: Two Visits

On this Botany job the first visit was to take the old lock off and nothing else. It came with me to the supplier so the replacement could be matched against the real part rather than a measurement. The match was a Whitco keyed unit — same mortise, same centres, same keeper.

The second visit was the quick half. The new lock went straight into the holes the old one came out of, the keeper on the jamb never moved, and the keys went to the owner. Nothing on the door was cut, drilled or filled.

What It Cost

$250 with the lock included, about two hours across both visits. The lock is the smaller part of that — most of it is the matching trip and the fitting.

It costs more when the original hardware is no longer made. Then the choice is a different unit and some adaptation to the door, and that is worth knowing before anyone starts rather than after.

One Honest Note on Security

A key changes what you can do with the door, not how strong the door is. You can lock the slider behind you on the way out, which a non-keyed handle does not allow at all. The glass, the track and the frame are exactly as they were. If you want the door itself harder to force, that is a conversation about the door — not about the lock.

See the full project — before, the match and after →