Do I need locks on every window?

Which windows genuinely need a key-operated lock, what the glazing standard adds beyond the lock, and how to keep escape routes usable.

Difficulty: beginner
Time: 45 min
Read: 4 min
Safety: caution

Short answer

Every accessible window is worth locking: ground floor, anything reachable from a flat roof, a garage roof, a bin store or a conservatory, and any window in an unlit or unoverlooked spot. Upper-floor windows with no climbing route are much less important. Use the lock that is there, keep the key nearby, and check your insurer's wording.

Most modern uPVC windows already have a locking handle fitted, and the commonest failing is not a missing lock but an unused one. The decision worth making is which windows to treat seriously, because the answer is about access rather than about which floor they are on.

Safety

Never lock a window that is a designated fire escape in a way that stops someone getting out. Keys must be to hand for everyone in the household, in the same place every time, and never on a hook visible through glass. In rooms with young children, a restrictor that limits opening is a fall-prevention measure as well as a security one.

What you'll need

Window lock keys — find them all first
Restrictors for child safety (optional)
Screwdriver for surface-mounted locks (optional)

Lock and glazing standards, and the risk each one addresses

Step by step

Walk the outside of the house and ask what you could reach.A flat roof over a kitchen extension, a garage roof, a wheelie bin, a conservatory, a boundary wall, a fixed ladder or a strong drainpipe all promote a first-floor window to an accessible one. That, not the floor number, is the test.
Locate every window key you own.Most houses have several and can find none. Group them, label them by room, and keep them in one consistent place out of sight of the glass but reachable in the dark.
Actually lock the accessible ones.A locking handle that is closed but not keyed still resists very little. Turning the key takes a second and it is what turns the handle into a lock.
Fit locks where there are none.Timber casements and older windows often have none. Surface-mounted casement locks and sash stops fit in fifteen minutes with a bradawl and a screwdriver and are inexpensive.
Deal with sash windows specifically.A traditional sash lock — a fitch fastener — holds the sashes together but little more. Sash stops, which are bolts through the upper sash that allow a few inches of ventilation and no more, are the practical answer and they also help with children.
Understand what the glass adds.A lock holds the frame shut; it does nothing about the pane. Laminated glass is what makes a glazed opening slow and noisy to get through, and that is the upgrade to consider on a vulnerable ground-floor window.
Check whether the beads are inside or outside.Internally beaded double glazing is the modern standard and is much better. Externally beaded units are usually secured by tape or clips inside; if yours are external and accessible, a glazier can advise on security glazing tape.
Set restrictors where you want ventilation and security together.A restrictor or a sash stop lets a window sit open a few inches. It is genuinely useful in hot weather and it means a ground-floor window is not left wide open in an empty room.
Keep the escape route usable.Bedrooms usually have a designated escape window. Everyone must be able to open it fast without hunting for a key. Where that is in tension with security, escape wins.
Read the insurance wording once.Policies frequently require accessible windows to be locked when the house is unoccupied. This is one of the more common reasons a claim gets argued about.

Tips

Windows left open on the latch in summer are the most common way an opportunist gets in. A restrictor lets you keep the airflow and remove the invitation.
Label window keys by room with a dot of coloured nail varnish rather than a tag that says which window it is.
If a handle turns but nothing locks, the gearbox inside the frame has failed. That is a repair, not a security purchase.

Common mistakes

Leaving keys in the window locks permanently — It converts a lock back into a handle, and a key visible through glass tells anyone outside exactly how little the window is doing.
Ignoring small windows — Toilet, utility and larder windows are small, often out of sight and frequently the only window in the house with no lock at all. Size is much less of an obstacle than people assume.

If it doesn't work

Handle turns freely and nothing locks

Cause: Failed espagnolette gearbox inside the sash — Fix: The gearbox is replaceable and the part is inexpensive. Until it is fixed the window is closed rather than locked.

Lost every window key

Cause: Common — they are small and rarely used — Fix: Most uPVC handle keys are one of a very small number of standard patterns and cost very little for a set. Take a photo of the handle to a locksmith or hardware shop.

Window will not lock without lifting the sash

Cause: Hinges or friction stays worn, so the sash has dropped — Fix: Replace the friction stays. Forcing the handle against a dropped sash wrecks the gearbox next.

Questions people ask

Do upstairs windows really need locking?

Only where there is a route to them. Check for flat roofs, garage roofs, conservatories, bin stores, sturdy trellis and boundary walls — those windows should be treated exactly like ground-floor ones. Genuinely unreachable upper windows matter far less.

Are trickle vents a security problem?

No. They are far too small to be a route in and they let you ventilate with the window closed and locked, which is a security improvement rather than a compromise.

Should I lock windows while I am at home?

Accessible ones, at night and when the room is unoccupied — particularly at the back of the house. During the day in a room you are in, it is your call. Insurance conditions usually bite when the property is empty.