How to protect patio doors, bifolds and windows from break-ins

To protect patio doors, bifolds and ground-floor windows, work in layers. Fit anti-lift devices and extra locks first. Then add an alarm contact with a shock sensor on each opening leaf, a curtain detector across the glass and, where the glass is plain, a glass-break detector. Finish with an outdoor camera fixed to the house wall, not one peering through the pane. Below we match an Ajax device to each job, with prices.

The Office for National Statistics' 2017 overview of burglary, from the Crime Survey for England and Wales, found that where a burglar got into a home, about seven in ten entered by a door and three in ten by a window.

Why are patio doors and bifolds a target?

A rear patio is often out of sight of neighbours and passers-by. An older slider without anti-lift protection can be raised off its track, and every bifold leaf has its own locks to attack.

Approved Document Q has applied to new homes in England since 1 October 2015 and sets standards for doors and windows to resist physical attack. The BSI says its PAS 24 test is the focus of that guidance. For an older door, look for a PAS 24 mark or ask its maker.

What should you fix before adding an alarm?

Locks buy time; the alarm raises the call. Check these first:

• Anti-lift devices: a stop in the head of the frame leaves no room to lift the sliding leaf out.
• Extra locking points: a second lock high or low on the frame, so the handle lock is not the only one.
• A security bar: a bar or pin across the track holds the leaf shut if the main lock fails.
• Bifold bolts: check the bolts on every leaf engage top and bottom.

A locksmith or the door's maker can advise on hardware.

Which sensor goes on the door itself?

A basic magnetic contact stays quiet until the leaf moves. The DoorProtect Plus with shock and tilt sensing adds an accelerometer, so blows to the frame or lock raise the alarm while the door is still shut. Shock sensitivity has three levels and a single knock can be ignored; the tilt sensor (5° to 25°) also guards a window left on its vent setting.

• Sliders: fit the detector to the fixed frame and the magnet to the moving leaf.
• Bifolds: fit a contact to each leaf that opens on its own.
• Indoors only: Ajax designs it for indoor use (IP50), so fit it inside.

The newer DoorProtect Plus U contact costs the same, ignores reed-switch chatter up to 0.15 seconds and can chime through an Ajax siren when a door opens while disarmed. For windows that only need an opening alert, DoorProtect U costs less. Ajax lists all three as Grade 2 under EN 50131, with PD 6662.

Do you need a glass-break detector as well?

The GlassProtect U glass-break detector has a microphone with a 180° field and works from 0.3 m to 9 m away, so one unit can cover several panes. Ajax rates it for 4 mm standard and insulated glass and 6 mm toughened glass, in panes at least 400 × 400 mm.

• Film: Ajax's GlassProtect specifications warn that it will not detect breaking glass covered with shockproof, sunscreen, decorative or any other film. Laminated glass is not on the GlassProtect U list either.
• Line of sight: a curtain or sofa between it and the glass deadens the sound; give it a clear view.

On filmed or laminated panes, rely on the shock sensor and a curtain detector. If the room also needs motion detection, CombiProtect U combines a PIR and a glass-break microphone in one case, though its glass list leaves out toughened glass.

How does a curtain detector cover a wall of glass?

A curtain detector watches a thin, flat slice of space, like an invisible sheet in front of the glass. Anyone crossing it sets it off and the rest of the room is ignored, so the doors can stay armed while you use the room.

Indoors, mount the MotionProtect Curtain at 2.4 m, as Ajax recommends; its 6° slice reaches up to 15 m, depending on settings. Outdoor models raise the alarm before anyone reaches the glass:

The DualCurtain Outdoor suits a long rear wall: mount it 0.8 m to 1.3 m high beside a door, or 0.5 m to 0.6 m above a sill for a window.

Where should a camera go?

• On the outside wall: behind glass, its own infrared bounces back off the pane after dark. Mount it high, with the door and the paving in front in view.
• Close enough to identify: Ajax gives an identification distance of 6.5 m for the 5 MP, 2.8 mm TurretCam and BulletCam, so keep the camera within about 6.5 m of the door.
• Smart alerts: both detect people, pets and vehicles and support a line-crossing rule. Ajax detectors can trigger them to record and send the clip to the app.

They run on PoE or 12 V and record to microSD or an NVR; see our Ajax cameras and NVRs and the CCTV buying guide. The ICO says data protection law applies when home CCTV captures beyond your boundary. Aim at your own property, use privacy filters or blockers where you can, and put up a sign. The ICO treats voices as personal information, so leave the built-in microphone off unless you need it.

What does a typical patio set-up cost?

One sliding door and two windows in the same room, added to an existing Ajax hub:

No hub yet? Choose one from our Ajax wireless alarm range; Hub 2 (4G) is £228.45. The camera also needs power and a memory card or recorder. Prices include VAT, delivery is extra, and prices can change.

Our take

Sort the locks first, then pick detectors that react to an attack on the frame or the glass, not only to the door opening. For a typical slider we would start with a DoorProtect Plus on the moving leaf and a curtain detector across the glass. GlassProtect U earns its place only where the glass is plain and unfilmed. A camera gives you evidence and an early look; on its own it stops nobody.

We are a supplier, not an installer, trading since 2012 from our Wolverhampton trade counter. We can recommend a qualified installer depending on the job and area.

Send us your door and window types for a parts list. Call 01902 902251 or contact us online. We ship nationally to England, Scotland and Wales.

Quick questions

Will a door contact work on a sliding patio door?
Yes, with the detector on the fixed frame and the magnet on the sliding leaf.

Can DoorProtect Plus go outside?
No. Ajax designs it for indoor use only. Outside, use an outdoor curtain detector.

Will a glass-break detector hear filmed glass breaking?
Ajax says GlassProtect will not. Use the shock sensor and a curtain detector instead.

Do curtain detectors ignore pets?
Ajax says to fit the indoor MotionProtect Curtain upside down to avoid pets. The outdoor Mini ignores animals up to 70 cm and the DualCurtain up to 80 cm.

Can a camera look through my patio door from inside?
Not well: after dark its infrared glares off the pane. Fit it on the outside wall.

Source: Ajax Systems blog, A simple guide to securing sliding doors, and Ajax product specifications. UK sources: ONS, Overview of burglary and other household theft; GOV.UK, Approved Document Q; Planning Portal, Part Q; BSI, PAS 24; ICO, Home CCTV systems.