What a triple lock is, and when a security door needs one

How a triple lock works: one lock, three points of hold

A triple lock pairs the main lock at the handle with two auxiliary locks, one above and one below, so the door is held along its full height. Amplimesh, a security screen maker, describes it as a lock that secures the door at three points with a one flick operation. The NSSA's description is the same in plain terms: a three point lock secures the door at the top, middle and bottom.

You can see the layout in the parts. Whitco's 3 point lock kit for its Leichhardt sliding lock comes with rods, two auxiliary locks, a keeper and screws. Kits for its Tasman MK2 hinged lock list auxiliary locks, rods and standard strikes. Whitco lists the Tasman MK2 as a mortice lock with an inside snib.

The main lock still does the everyday work. On the Tasman MK2 it latches automatically, takes the key, and the key overrides the snib. The two extra points cover the top and bottom of the door, the parts the NSSA says a three point lock helps stop being wrenched open.

Single or triple locking: triple is standard on a compliant door

A single lock holds a security door at the handle only, while a triple lock adds a hold near the top and bottom corners. The NSSA puts the difference in one line: a three point lock is likely to prevent the bottom or top of the door being wrenched open.

Single point locks are still sold. Whitco's Tasman MK2, for example, is listed as a single or multi point hinged security door lock, with 3 point kits available for additional security. ScreenGuard's cost guide says a single-point lock is the simplest option, while multi-point or triple-lock mechanisms add cost.

The NSSA's position is that a compliant security door comes with three points as standard. Its FAQ says security doors must pass testing to Australian Standards, and that this almost always means a three point lock. If a quote lists a triple lock as an optional upgrade, ask whether the door has been tested and labelled to AS 5039 without it.

Hinged and sliding doors: both can lock at three points

Hinged and sliding security doors can both be fitted with three point locking; the lock body is different, the principle is the same. ScreenGuard says its hinged doors take a three-point lock, and its French doors use multi-point locking across both leaves.

For sliders, Whitco's Leichhardt is a single and multi point mortice sliding security door lock, with optional kits for 2 and 3 point applications. It has a parrot beak deadlock, and it can only be key locked or snibbed when the door is fully latched. That last detail matters on a patio slider: a door that looks shut but hasn't caught won't lock. Our guide to securing a sliding glass door covers the patio bolts and anti-lift steps for the glass panel behind the screen.

The ranges we build follow the same idea. PERFGUARD, the perforated aluminium range we make, has hinged and sliding doors tested using three point locking hardware. Our guide to hinged versus sliding security doors covers the rest of that choice, from swing space to track upkeep.

The cylinder: five pins, and one key for every door

The cylinder is the part the key turns, and the NSSA says key locks should be a five pin cylinder as a minimum. It's worth checking on a quote because the cylinder can be sold separately from the lock body. Whitco, for one, lists lock bodies supplied with no cylinder, and a separate cylinder to suit its Leichhardt sliding, Tasman and Tasman Escape locks.

Keyed alike means several cylinders cut to work with the same key, so one key opens the front door, the back door and the patio slider. Whitco states its 5 pin C4 cylinder can be keyed alike to other Whitco 5 pin C4 cylinder locks, and lists keyed alike packs of up to 50. Amplimesh gives the same answer to whether several doors can share a key: it's done with a keyed alike cylinder fitted into each lock.

Whitco's keyed alike statement covers its own 5 pin C4 cylinders, so ask before mixing lock brands across doors. ScreenGuard notes that keyed-alike systems across multiple doors add cost, so raise it at the measure rather than after the doors are made.

Deadlocking: what Queensland police advise

Queensland police advice favours deadlocks on the doors you go in and out of. Townsville police list deadlocks as the type of lock to use on entry and exit doors, and say to lock doors with a key even when you're home. Their advice also covers screens directly: consider security screen doors designed and installed to Australian standards, lock them with the keys, and never leave the keys in the lock.

Closer to home, police in the greater Cairns area have encouraged residents to make sure security screens and doors are locked and secured using fitted dead bolts.

Whitco's Leichhardt sliding lock, for example, deadlocks by key from both sides. Ask how the lock on your quote deadlocks, and from which side. Our article on whether security screens stop burglars covers what the research says about locked screens.

Escape locks: when a room has to open from inside

Some openings need a lock that always lets you out from inside. ScreenGuard says that if a room needs a legal means of escape, a standard multi-point lock isn't always the right fit.

Escape locks exist for that case. Whitco's Tasman Escape is an emergency escape hinged security door lock, free to exit at all times, and it's available with an optional 3 point kit. So a door can lock at three points and still open from inside without a key.

Which rooms need a means of escape is a building compliance question for your house and isn't something to decide from a guide. Mention bedrooms with only one way out, granny flats and any door you'd rely on in a fire when we measure, and we'll talk through lock options for each opening.

Adding a three point kit to an existing door: often possible, ask first

A security door with a single point lock can often be upgraded to three points, as long as its lock is one that takes a multi point kit. Whitco's Tasman MK2 and Leichhardt locks both list optional 3 point kits, and the Tasman MK2 retrofits the previous Whitco Tasman lock. Whether a particular door can take a kit depends on the lock fitted to it and on the door itself, so have it looked at before you buy parts.

Fitting a kit is installer work. A kit adds rods and auxiliary locks, plus a keeper or strikes, to the door and frame. The NSSA says compliant security doors are made and installed to very tight tolerances with specialised fixings, and that in many states security screen installers need to be licensed.

We replace triple locks, patio bolts, lock cylinders and complete locks as onsite repairs. If a triple lock you already have is catching at one point only, our guide to a security screen door lock not working covers the checks to make first.

What to ask before you sign a quote

Ask these questions about the lock for every door on the quote, hinged or sliding. The answers decide most of how the door will hold up, and they're easier to settle before the door is made than after. Our security doors page sets out the four ranges we make to measure in Cairns, and our guide to choosing security screens in Cairns covers the mesh and frame side of the same decision.

• Is three point locking standard on this door, or priced as an extra?
• Is the door tested and labelled to AS 5039, with the lock it was tested with?
• Does the cylinder have at least five pins?
• Can every door on the quote be keyed alike to one key?
• How does the lock deadlock, and can it be key locked from both sides?
• Does any room need an escape lock that opens freely from inside?
• On a slider, will it only lock once it's fully latched?
• Does a hinged door have at least three fixed-pin hinges, as the NSSA recommends?