1. Fit multi-point locking systems
Multi-point locking systems engage bolts at several points along the window frame, usually at the top, bottom and middle. This makes them far more resistant to forced entry than a single central catch. The industry standard to look for is PAS 24, a test that simulates real-world break-in attempts. Secured by Design, the UK police flagship initiative, recommends PAS 24 as the minimum benchmark for new or replacement windows. Replacing a basic lock with a multi-point system costs between £80 and £250 per window, depending on the frame type and window size (Secured by Design, 2026).
- Engages at least three locking points along the frame
- PAS 24 testing is the recognised security standard
- Cost typically £80–£250 per window
2. Install laminated glass
Laminated glass consists of two panes bonded together with a tough plastic interlayer. If the glass is struck, the interlayer holds the pieces in place, preventing an intruder from reaching through. This type of glazing meets BS 6206, the British Standard for security glazing. FENSA, the competent person scheme for window installations, advises that laminated glass is appropriate for ground-floor windows and doors where impact resistance matters most. Replacing a single pane with laminated glass costs roughly £150–£400 per window, depending on the size and frame type (FENSA, 2026).
- Plastic interlayer stops the glass from shattering into a hole
- BS 6206 is the relevant British Standard for security glazing
- Cost typically £150–£400 per window
3. Add window restrictors to upstairs windows
Window restrictors limit how far a casement or sash window can open, typically to around 100mm. This serves two purposes: it prevents intruders from climbing in through an open window, and it is a key child safety measure. For security, choose restrictors that are tested to BS 3621, the standard for thief-resistant locks. TrustMark, the government-endorsed quality scheme, recommends checking that restrictors are fitted by a registered installer. The cost for a single restrictor is between £15 and £50, including fitting (TrustMark, 2026).
- Limits the opening gap to around 100mm
- BS 3621-tested restrictors offer proven forced-entry resistance
- Cost typically £15–£50 per window
4. Apply security film to existing glass
Security film is a clear polyester layer that bonds to the inside of the glass. It does not make the glass unbreakable, but it holds the fragments together after impact, delaying an intruder by 30 to 60 seconds. This delay can be enough to deter a casual burglar. Security film is a low-cost option, typically £5 to £20 per square metre, and can be applied to existing windows without replacing the frame or glass. TrustMark advises that professional installation gives the best adhesion and durability (TrustMark, 2026).
- Bonds to the glass surface and holds fragments together
- Delays forced entry by 30–60 seconds
- Cost typically £5–£20 per m²
5. Fit sash jammers on sliding windows
Sash jammers are small metal devices fitted to the frame of a sliding sash window. When engaged, they prevent the window from being slid open, even if the main lock is forced. They are a practical upgrade for older sash windows that cannot easily accommodate a multi-point lock. Secured by Design specifically recommends sash jammers for traditional timber sash windows. The cost is roughly £20 to £60 per window, depending on the finish and whether you fit them yourself or use a tradesperson (Secured by Design, 2026).
- Locks the sash in place, preventing sliding movement
- Recommended for older sash windows by Secured by Design
- Cost typically £20–£60 per window
6. Upgrade to key-operated handles
A key-operated handle stops an intruder from turning the handle from outside, even if they break the glass. This is a simple swap on most uPVC and timber windows. Look for handles that have been tested to BS 3621, which assesses resistance to forced turning and lock picking. Secured by Design lists key-operated handles as a basic but effective security upgrade. A replacement handle costs between £15 and £40, and fitting is straightforward for a competent DIYer or a local locksmith (Secured by Design, 2026).
- Prevents handle operation from the outside
- BS 3621 handles offer tested resistance to forced turning
- Cost typically £15–£40 per handle
7. Install internal window bars or grilles
Internal bars or grilles create a physical barrier inside the window recess. They are fixed to the frame or wall and can be hinged or removable for cleaning and emergency escape. Fire safety regulations must be considered: any bar or grille fitted to a bedroom window must be openable from the inside without a key. GOV.UK guidance on fire safety in the home stresses that escape routes must not be blocked. The cost for a set of internal bars is £50 to £200 per window, depending on the material and whether they are custom-made (GOV.UK, 2026).
- Creates a physical barrier inside the window recess
- Must comply with fire safety regulations for escape routes
- Cost typically £50–£200 per window
8. Use hinge-side security bolts
Hinge-side bolts are small metal pins fitted into the hinge side of a casement window. They prevent the window from being lifted off its hinges, a common method of forced entry on side-hung windows. These bolts are discreet and can be retrofitted to most existing windows. Secured by Design recommends them as a low-cost addition to any casement window that does not already have hinge protection. The cost is typically £10 to £30 per window, making them one of the cheapest security upgrades available (Secured by Design, 2026).
- Stops the window being lifted off its hinges
- Effective on side-hung casement windows
- Cost typically £10–£30 per window
9. Add external security lighting
Motion-activated security lights placed near windows can deter intruders by removing cover of darkness. Lights should be positioned to illuminate ground-floor windows and any side or rear access points. Installation must comply with BS 7671, the wiring regulations. TrustMark recommends using a registered electrician for any new external lighting circuits. A single PIR floodlight costs between £30 and £100, plus installation. This is not a lock or barrier, but it is a proven deterrent that works alongside physical security measures (TrustMark, 2026).
- Motion-activated lights remove cover of darkness
- BS 7671-compliant installation is required
- Cost typically £30–£100 per light
10. Check and replace worn window seals
Deteriorated rubber seals around a window frame can create gaps that weaken the overall security of the lock mechanism. A loose seal can also make it easier to insert a tool to force the window open. Replacing worn seals restores the tight fit of the frame and improves energy efficiency by reducing draughts. The Energy Saving Trust notes that replacing seals on existing windows can cut heat loss and lower energy bills. The cost is low, typically £5 to £20 per window for the seal material (Energy Saving Trust, 2026).
- Worn seals create gaps that weaken frame security
- Replacing seals also improves energy efficiency
- Cost typically £5–£20 per window
Your window security should match the risk level of each room – ground-floor and easily accessible windows need the strongest protection. Focus on locks, glass strength, and restrictors for upper floors, and always look for products tested to British Standards or Secured by Design accreditation.
For more information on choosing the right windows for your home, read our guide on how to choose replacement windows for security and energy efficiency. If you are considering new windows, also see double glazing costs and grants in 2026 and how to find a FENSA-registered window installer.
Frequently Asked Questions
A multi-point locking system tested to PAS 24 is the best option, engaging at least three points along the frame. Secured by Design, the UK police initiative, recommends this as the minimum benchmark for new or replacement windows.
Costs range from £80–£250 per window for a multi-point locking system to £150–£400 per window for laminated glass. Prices depend on frame type and window size, according to FENSA and Secured by Design.
Yes, window restrictors limit opening to around 100mm, preventing intruders from climbing in. Choose restrictors tested to BS 3621, the standard for thief-resistant locks, as recommended by TrustMark.
PAS 24 is a test that simulates real-world break-in attempts on windows. It is the industry standard for security and is endorsed by Secured by Design as the minimum benchmark for new or replacement windows.
Yes, laminated glass holds together when struck, preventing intruders from reaching through. It meets BS 6206, the British Standard for security glazing, and is recommended by FENSA for ground-floor windows.
