How to Secure Sliding Doors: 6 Options Ranked

October 2026, by Florin Ristea, General Manager.

Fit a locked barrier on the inside of the sliding door. A retractable trellis door is the strongest everyday option because the glass stops being the only line of defence. Then stop the sliding panel from being lifted off its track and keep its own lock in use. Light and an alarm sensor come after that.

Why sliding doors are the weak point

A sliding patio door is the widest opening in most houses and is mostly glass. Its own catch holds the panel to the frame, not the panel to the track, so a panel that can be lifted can often be lifted out. Patio doors also face the garden, where nobody on the street can see what happens.

Six ways to secure a sliding door, ranked

	What it stops	What it does not stop	Use it when
1. Retractable trellis door inside the slider	Entry after the glass breaks or the panel is lifted out	Damage to the glass itself	Always the first step on a ground-floor or easy-to-reach slider
2. Sliding security gate	The same, with a solid sliding barrier	Damage to the glass	There is side space for the gate to slide into
3. Anti-lift block or screws in the top track	The panel being lifted off its track	Breaking the glass	On every slider, as a cheap extra
4. A bar or dowel in the bottom track	The panel being slid open from outside	Lifting or breaking	As a backup while you are home
5. An extra lock on the door panel	Forcing the existing catch	Breaking the glass	The original catch is worn or loose
6. Lighting and an alarm sensor on the door	Nothing physically; they make an attempt noticed	Entry	Together with a barrier, never instead of one

The first two put metal between the house and the garden. The other four improve the door you already have. Most homes need one from the top two and one or two from the rest.

What makes a trellis door work on a slider

The trellis door is fitted on the inside of the frame, folds to one side when you want the doorway open and locks across it at night. On a slider, three details decide how well it works:

The tracks. The Deluxe Trellis Door runs on an aluminium top and bottom track with stainless roller bearings. The bottom track has to sit flat on the threshold, which is why the measurer checks floor level and drainage at the opening.
The locks. Robo Door retractables take a slam lock, a deadlock or both, with up to three locks per door. Hook locks have an anti-lift pin and every lock comes with three keys. Keyed-alike locks are available if you want one key for every door.
Reaching the cylinder. On the Deluxe, a security pin and the handle design keep the lock cylinder out of reach through the trellis. The DuPlus uses a lock-keep design for the same reason.

Stacking space matters too. A folded trellis door needs room beside the opening, so the measurer records it and tells you which side it should fold to.

Which trellis door for a patio slider

	Built as	Manufacturing warranty	From
Deluxe Trellis Door	Every upright slotted and riveted; heavier steel than Econo	10 years, plus the 5-year Break-In Repair Guarantee	R4,500
Alu-Deluxe Trellis Door	All aluminium, for coastal homes	10 years	Quoted to the opening
DuPlus Trellis Door	Double steel uprights, all steel	5 years	Quoted to the opening
Econo Trellis Door	Every third upright slotted and riveted, for a lower price	5 years	Trellis doors from R3,500

For a slider you use every day and leave open in summer, the Deluxe is the strongest choice in the range and the only one with the Break-In Repair Guarantee. Within 500 metres of the sea, choose the Alu-Deluxe or ask for galvanising on a steel door. Trellis doors are made in five to seven working days; the DuPlus takes ten to fourteen.

The cheap fixes, done properly

An anti-lift block is a small stop or a pair of screws in the top track, set so the panel can still slide but cannot rise far enough to leave the track. Check it does not foul the panel when it slides. A dowel in the bottom track works only when you remember to put it in, so treat it as a backup. If the original catch is loose, have it replaced before adding anything else; a second lock on a worn frame does little.

Keep a way out

Every locked barrier is also a barrier for you during a fire. Keep the trellis door keys in the same place every night, close to the door but out of reach from outside. If the slider is your main exit from a bedroom wing, plan another route before anything is made.

What no barrier promises

Our terms are plain about this: Robo Door products are security barriers and do not guarantee that a crime or forced entry will be prevented. What a good barrier does is buy time and make entry slow and noisy. Combine it with lighting and an alarm, and use it every night.

For the measuring detail on patio doors, read trellis doors for sliding patio doors. For the choice between lock types, read slam lock or deadlock.