Residential Security
French doors do not usually fail at the lock. They fail at the middle, where the two doors meet. A single entry door bolts into a solid frame; a pair bolts into each other, and the inactive leaf is only held by the flush bolts at its top and bottom. Get those bolts right, put a multi-point or a properly anchored deadbolt on the active leaf, and a French door is as secure as anything else in the apartment. Leave them loose and the best cylinder on the market protects nothing.
Think about what the lock is biting into. On a normal door, the bolt goes into a strike that is screwed into a jamb that is nailed into the building. There is a wall behind it. On a pair of French doors, the active leaf locks into the inactive leaf - a second door, hanging on its own hinges, held in place only by two bolts shot into the head and the sill.
That is the whole story of French door security. If the top and bottom bolts are thrown into solid strikes, the inactive leaf becomes part of the frame and the pair behaves like a single strong door. If the bolts are missing, bent, painted shut, or landing in a hole somebody drilled into a wooden threshold years ago, the pair can simply be spread apart at the middle with steady pressure, and the lock goes along for the ride still locked.
The second difference is the glass, and it matters less than people assume - but for a specific reason worth understanding, which we come to below.
Describing the problem accurately gets you the right fix, so it is worth knowing what the installer or locksmith is talking about.
A multi-point lock is the honest upgrade for a French or terrace door. Lift the handle and bolts engage at the top, the middle and the bottom of the leaf at once. Because the force of a pry attack has to be defeated at three widely separated points rather than one, the door cannot be bowed open at a single spot - which is exactly how a tall, relatively slender door normally gives way.
The practical catch is that multi-point hardware is usually matched to the door. Fiberglass and vinyl patio doors are frequently built for it and can take a direct replacement. A wood pair from a renovation twenty years ago often cannot, because the stile is too narrow or the edge was never routed for a gearbox. In that case the sensible answer is not to force it: a strong single deadbolt landing in a reinforced strike, plus serious bolts on the inactive leaf, gets most of the benefit.
If your pair is also sagging or dragging, fix the geometry before you buy hardware. A multi-point on a door that does not sit square will never engage all its points, and you will have paid for a lock that throws one bolt - see when a door will not lock properly.
We install and repair French door hardware across the five boroughs - multi-point locks, flush bolts, deadbolts in narrow stiles, reinforced strikes and realignment on doors that have dropped. We will tell you honestly when a door can take a multi-point and when it cannot. Licensed NYC locksmith, NYC DCA #1362785-DCA.
If you only do one thing to a French door, do this one. The inactive leaf has to be genuinely locked into the structure, not resting against it.
People assume glass is the weakness, and the instinct is half right. Breaking a pane is loud, slow and leaves evidence, so it is not usually the first move. The real risk is narrower: whether breaking one small pane puts a hand within reach of something that unlocks the door.
That is why an inside thumbturn sitting a few inches from a divided-light pane deserves a look, and why the fix is placement and glass rather than a keyed cylinder on the inside. Security film on the panes nearest the lock, laminated glass if you are replacing anyway, or hardware relocated out of reach all solve it without creating a door your family cannot get out of in a fire. A key-both-sides deadbolt on a door people use is the wrong trade, for the same reasons set out in jimmy-proof and police locks and improving apartment door security.
Most French doors in New York City are not front doors - they open onto a terrace, a setback, a rear garden or a balcony - and that changes two things.
First, access. A ground-floor garden door behind a brownstone, or a terrace reachable from a neighboring setback or a fire escape landing, is a far more realistic target than one twenty floors up with no adjacent access. Walk out and look at how somebody would actually reach the door; that answer should set how much hardware you buy. The same thinking applies to windows at the same level - see window lock security in a NYC apartment and sliding glass door security if some of your openings slide rather than swing.
Second, permission and egress. Co-ops and condos commonly control anything that changes the look of a terrace door or facade, so confirm the house rules before drilling - see changing locks in a co-op versus a condo. And if the terrace or balcony connects to a fire escape or a required exit route, the door must open from inside without a key or tool. That is not a preference; it is the line that governs every lock on an exit path in this city - see fire escape door lock requirements in NYC.
Interior French doors - parlor doors, office doors, a pair between living room and study - are about privacy and sound, not security. They typically carry a passage or privacy set, and the right hardware is whatever operates smoothly and latches quietly. Do not spend security money there. If the goal is keeping a room genuinely closed, that is a separate conversation about the room's own door - see interior door lockouts for what to do when one of these jams with someone on the wrong side.
If a French or terrace door has already been forced, secure the opening first and document before repairing - what to do after a break-in covers the order. New York City licenses locksmiths; ours is NYC DCA #1362785-DCA, and verifying a locksmith license takes a minute before you let anyone work on your doors.
Not inherently, but they fail differently. A single door locks into a solid frame on both sides, while a pair of French doors locks into each other at the middle. That meeting point is only as strong as the bolts holding the inactive leaf, so a pair with weak flush bolts can be spread apart even though the lock itself never fails.
A multi-point lock on the active leaf plus proper flush bolts top and bottom on the inactive leaf. The multi-point throws bolts at several heights so the door cannot be levered at one spot, and the flush bolts turn the inactive leaf into part of the frame. On a wood pair that cannot take a multi-point, a surface-mounted deadbolt into a reinforced strike is the practical fallback.
Usually yes, on the active leaf, as long as there is enough stile width beside the glass to take the cylinder and bolt. Narrow-stile doors may need a narrow-backset deadbolt or a different approach. The bolt also has to land in a strike that is anchored into framing, not just into the edge of the other door.
No, and in most homes they should not have one. A door people use to get out needs to open from inside without hunting for a key. Use a thumbturn, and if the glass is close enough that someone could reach the turn after breaking a pane, address the glass or the reach rather than adding an inside keyway.
Secure it the same way as any exterior door - a real deadbolt or multi-point, bolts on the inactive leaf, and a lock that does not need a key from inside - and check your building rules before changing anything visible, since co-ops and condos often control the appearance of terrace doors. If the terrace connects to a fire escape or a shared setback, the door may also sit in an exit path, which rules out anything that locks from the inside.
Yes, and misalignment is the most common call on a pair. Doors sag, the astragal rubs, the flush bolts stop reaching their strikes and people stop throwing them. That is an adjustment and hardware job rather than a new door. Call (718) 412-1332 and tell us whether the problem is at the top, the bottom or the middle.