Window Security: The Overlooked Weak Point in Most Homes

Here is something I see all the time: someone calls me out to fit a brand-new anti-snap cylinder on their front door — a proper upgrade, good lock, well fitted. Then I walk round the back of the house and find ground-floor windows with cockspur handles from 1998 that a child could open with a butter knife.

Your front door might have the best lock money can buy, but if your windows are easy to open, you have left the burglar a perfectly good alternative route in. Windows account for around 22% of residential burglary entries in the UK, and in most of those cases, the window was either unlocked, poorly locked, or had a lock so weak it might as well have been unlocked.

Window Lock Types: What Is on Your Windows?

Cockspur Handles

These are the T-shaped handles found on older uPVC windows. You turn the handle to close the window, and that is it — no key, no additional locking point. They are held closed by a small spur that hooks over a receiver on the frame.

The problem: they can be forced open with a flat tool inserted between the window and frame. On older windows where the frames have warped slightly, they sometimes do not even engage properly.

Verdict: Replace with locking handles or add sash jammers.

Espagnolette Handles (Locking Handles)

These are the standard locking handles on modern uPVC windows. Turn the handle to close, then lock with a key. They operate an espagnolette bar — a metal rod that extends up and down to engage locking points at multiple positions in the frame.

When working properly, these are decent. The issue is that the mechanisms wear out. If you turn the handle and it feels loose, or the key turns but does not feel like it is locking anything, the mechanism may have failed.

Verdict: Good when working. Get the mechanism checked if the handle feels loose or the lock does not engage. I repair and replace these regularly across Coventry — see our [uPVC lock repair service](/services/upvc-lock-repair).

Sash Jammers

A sash jammer is a small swivelling bolt that mounts on the inside of the window frame and flips up to block the window from opening. They are simple, cheap, and surprisingly effective as an additional locking point.

They work on uPVC casement windows and tilt-and-turn windows. Crucially, they are visible from outside, which tells a potential burglar that the window has an extra lock they will need to deal with.

Verdict: Excellent as a secondary lock. Fit them to all ground-floor windows and any first-floor windows accessible from a flat roof, extension, or bin. Around £10-£15 per window fitted.

Window Restrictors

Window restrictors limit how far a window can open — usually to about 100mm. They are primarily a child safety device, but they also have a security benefit: they allow ventilation in warm weather without leaving the window wide enough for someone to climb through.

Verdict: Useful for upstairs windows and for ground-floor ventilation in summer. Not a substitute for a proper window lock.

Cable Window Restrictors

A more robust version of the basic restrictor. A steel cable limits the opening distance and requires a key to release. More secure than plastic restrictors.

Verdict: Good for windows you want to leave partially open regularly.

How Old Windows Are Vulnerable

Older uPVC windows (pre-2004 or thereabouts) have several weaknesses:

If your windows are from the early 2000s or before, they deserve a careful check even if the locks seem to work.

uPVC Window Lock Upgrades

Upgrading the locks on your existing uPVC windows is significantly cheaper than replacing the windows themselves. Here is what I typically recommend and fit:

Replacement Locking Handles

If your cockspur handles are old, replace them with modern locking handles. These are key-operated and provide a positive lock. From £15-£25 per window fitted, depending on the type.

Sash Jammers

As described above — about £10-£15 per window fitted. I usually recommend fitting these alongside new handles for a two-point locking setup.

Window Lock Bolts

Small key-operated bolts that fit into the frame of the window. They provide an additional locking point independent of the main handle mechanism. About £10-£15 each fitted.

Espagnolette Gearbox Replacement

If your locking handle works but the mechanism inside the window does not engage properly, the espagnolette gearbox may need replacing. This is the metal unit inside the window edge that the handle operates. Replacement costs from £45-£75 per window fitted, which is far cheaper than a new window.

Sash Window Security

Traditional sash windows in older Coventry homes (particularly in areas like Earlsdon, Chapelfields, and Stivichall with Victorian and Edwardian housing) present their own security challenges.

Common Sash Window Vulnerabilities

Sash Window Lock Options

For period properties, these locks can be fitted sympathetically without damaging the character of the windows.

Which Windows to Prioritise

Not all windows carry the same risk. Here is how to prioritise:

High Priority

Medium Priority

Lower Priority

Cost of Window Lock Upgrades

Here are typical costs for window security upgrades across Coventry. These include supply and fitting:

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For a typical 3-bedroom semi in Coventry with 4-5 ground-floor windows, a full window lock upgrade with locking handles and sash jammers costs around £100-£175 total. That is a fraction of the cost of one new window, and it makes a genuine difference to your security.

Check the full [price list](/prices) for our complete range, or combine a window lock upgrade with a [front door lock change](/services/lock-change) for a full home security improvement.

Do I Need to Replace My Windows?

In most cases, no. If the frames are structurally sound, the seals are intact, and the glass is not cracked, upgrading the locks is far more cost-effective than replacing the whole window. New uPVC windows cost £300-£600 each fitted — upgrading the locks on your existing windows costs a fraction of that.

The exceptions are if your frames are rotten (wooden windows), severely warped, or the sealed units have blown (condensation between the glass panes). In those cases, new windows make sense for thermal and security reasons.

What to Do Next

Walk around your home and check every window. Can you lock each one with a key? Do the locks actually engage? Are any ground-floor windows especially vulnerable?

If you are in Coventry or the surrounding areas and want me to check your windows and give you an honest assessment, call 07735 336175. I carry the most common window lock types in my van, so in most cases I can upgrade your windows on the spot during a single visit.

You can also read the full [home security checklist](/blog/home-security-checklist-2026) for everything else to check while you are at it.