Window Won't Lock? 6 Fixes, from Free to a New Latch

The latch spins loose. Or the crescent latch stops short of the keeper. Or the catch on the slider snapped off before you moved in, and a broom handle in the track has stood in for it ever since. Whichever it is, the window is shut and not locked, and you'd like that settled before bed.

A window latch is a small part, and every fix for it is small too. One costs nothing. Two clamp on in seconds. Two screw on in minutes. One is a hardware-store trip. This guide runs them cheapest first and ends with the one layer that doesn't care whether the latch works.

To fix a window that won't lock: close the sash fully, clear paint from the keeper, tighten its screws; if the latch is broken, a $14.99 clamp-on sash lock pins the window shut, no drilling.

Locks are half the job. The other half is the glass, which no latch protects, and for that we make the TremShield Vibration Sensor Alarm, a $29.99 siren that sticks to the pane and fires when someone pries or strikes it. It comes last. Locks first.

Fix 1, free: three checks before you buy anything

Do these in order, with the room light on. None of them takes long.

1. Is the sash all the way closed? On a double-hung window (the up-and-down kind), a top sash that has slipped down leaves the crescent latch swinging short of the keeper. Push the top sash up with both palms, push the bottom sash down, and try again. On a slider, run a finger along the track: grit stops the panel closing the last bit.
2. Is paint in the keeper? A window painted with the latch open ends up with a keeper full of dried paint. Scrape it out with a utility knife.
3. Is the keeper or the latch loose? Tighten the screws on both. If a screw turns and never bites, the hole is stripped: back it out, push in a wooden toothpick or two with a dab of wood glue, snap them flush, and drive the screw again.

If the lever spins with no resistance at all, the latch has broken inside and tightening won't bring it back. That's a replacement (fix 6). Until the part is in your hand, fix 2 holds the window tonight.

Fix 2, $14.99: how do I lock a window with a broken latch?

Leave the latch alone and add a lock that never touches it. Our Window Sash Lock comes two to a pack for $14.99. The lock is a small clamp tightened by a padded thumb-screw. For a double-hung window, slide it onto the frame just above the lower sash and turn the screw until it bites. The sash can't be lifted past it. On a slider, it clamps to the track and the panel can't move.

No drilling, no tools, no marks. Loosen the screw and it comes off whenever you want the window open. Set it against the closed sash and the window is locked shut. Set it a few inches up and the window vents and stops there; the gap can't be pushed wider from outside.

The broken latch stays broken and no longer matters. Two in the pack: the bedroom and the bathroom, or the two windows the street can't see.

Fix 3, $14.99: how do I lock a sliding window with a broken catch?

A slider has a second weakness the catch never solved: on many of them, someone outside can lift the panel clear of its track without touching the latch. The broom handle stops the slide and does nothing about the lift.

Our Sliding Window Lock ($14.99) clamps to the track itself and holds the panel down as well as sideways: it can't slide and it can't be lifted clear. Wipe the track, set the lock where you want the panel to stop, tighten the thumb-screw (there's an adhesive base too). About ten seconds. Fully shut, or a vent gap you choose.

If the factory catch still works, keep using it; two locks on one window beat one. On a full-size patio door this lock grips the track too, but the main overnight lock there is a track bar. Our sliding glass door guide covers that.

Fix 4, $19.99: should I put a keyed lock on the window?

On a window nobody will ever climb out of, yes. A latch with a thumb-turn is a latch a hand can flip, and a hand can arrive through a broken corner of glass. A window lock with key takes that option away: the window unlocks only with the key in your pocket.

Plainly: this one screws on. Hold the lock and keeper where the two frames meet at the rail, mark the holes, drill pilots, drive the included screws. About five minutes per lock. The pack is two locks keyed alike, one key for both, $19.99. It fits most double-hung and sliding windows (the two frames need to overlap at a rail), white, no batteries.

Never put it on an escape window. If a window is the way out of a bedroom in a fire, a lock that needs a key found in the dark is the wrong lock for it. Use it on the basement window, the garage window, the one behind the shed. Renters: the small screw holes patch over easily, but check the lease before you drill.

Fix 5, $19.99: how do I lock a window and still open it for air?

The sash lock and the track lock both hold a vent gap, so a double-hung or a slider is already covered. The restrictor is for the windows those clamps can't fit: a casement (the crank-out kind) has no track and no overlapping sashes to clamp onto, and a nursery window wants a stop a small child can't undo.

Our Window Restrictor Lock ($19.99) is a steel cable between two brackets, one screwed to the frame and one to the opening sash. The window opens roughly four inches and stops, too narrow to climb through. A key releases the cable so the window opens fully for cleaning or for getting out. It screws on in a few minutes, suits most opening windows including casement and sliding sash styles, and the small holes patch over if you move it.

If the restricted window is also a way out, hang the key beside the window, where a hand through the gap can't reach it. Not in a drawer across the room.

Fix 6: how do I replace the window latch itself?

The permanent fix, and a hardware-store trip rather than a purchase from us. Unscrew the old latch and keeper and take both with you. Match three things: screw-hole spacing, hand (which way the lever swings), and style (crescent latch or slider catch). Note the maker's name on the frame too, in case the part is specific to that maker.

The window is unlocked from the moment the old latch comes off until the new one goes on. A clamp-on lock covers that gap, and nothing says you have to make the trip at all.

The layer that doesn't need the latch at all

Every fix above holds the sash. None of them does anything about the pane, and glass breaks from outside without anyone touching a lock.

The TremShield Vibration Sensor Alarm covers the pane. Peel the backing, press it onto the glass, and the install is done in about 60 seconds. Pry at the pane or hit it and the glass vibrates; the alarm picks that up and fires a 125 dB siren while the pane is still in one piece. A sensitivity dial lets you tune it: a passing truck stays quiet, a deliberate strike does not. It needs no Wi-Fi and no app, and there's no monthly fee. It peels off cleanly, and moving it to another window takes a fresh mounting pad.

Two limits. It guards the pane it's stuck to, so each window you want covered gets its own. And it's a siren, not a lock: it doesn't hold the sash, which is why it pairs with a clamp lock rather than replacing one.

Which fix for which window?

Window won't lock FAQ

Why won't my window latch lock?

Usually one of three things: the sash isn't fully closed so the latch misses the keeper, dried paint is filling the keeper, or the latch or keeper screws have worked loose. Close the sash hard, scrape the keeper, tighten the screws. A latch lever that spins with no resistance has broken inside and needs replacing.

How do I lock a window with a broken latch?

Clamp on a lock that doesn't use the latch. A clamp-on sash lock tightens by thumb-screw onto the frame above the lower sash, or onto the track of a slider, and the sash can't move past it. No drilling, no tools, shut or at a vent gap. The TremShield Window Sash Lock is $14.99 for two.

Can I lock a window without drilling?

Yes. A clamp-on sash lock and a sliding window track lock both tighten by hand with a thumb-screw and leave no holes, so they suit rentals. A vibration alarm sticks to the glass with adhesive and peels off. Keyed window locks and cable restrictors screw on, so those need a drill and, in a rental, the landlord's OK.

Is it safe to put a keyed lock on a bedroom window?

Only if that window is not the way out in a fire. A keyed lock can't be opened without the key: the point against a hand through broken glass, the problem in a smoke-filled room. Put keyed locks on basement, garage and other windows nobody would climb out of, and a clamp-on lock that loosens by hand on any escape window.

Does a window alarm work if the lock is broken?

Yes. A vibration alarm sticks to the glass and fires when the pane is pried or struck, so it doesn't depend on the latch at all. It won't hold the window shut, though. It's a siren, not a lock, so pair it with a clamp-on lock: the lock holds the sash and the alarm guards the glass.

Lock the sash tonight, then cover the glass

Do the free checks now. If the latch is dead, clamp a sash lock or a track lock on before bed and sort the replacement part when you get to it. That's the window held shut.

Then the glass. The 6-pack at $99 puts an alarm on six panes at $16.50 per alarm, which is $80.94 under the price of six singles, and it ships with two free no-drill window locks and the Home Security Guide (a PDF), so two of the windows on your list get their lock in the same box. Free US shipping and 30-day returns. A lock holds the sash. The alarm guards the glass. Do both tonight.