Smart lock for French doors: which leaf gets the deadbolt

A pair of French doors looks like one door cut down the middle, so the natural assumption is that a smart lock goes on each half the way it would on any front door. It doesn’t. One leaf of the pair almost always stays shut by something that has nothing to do with a lock, and the keypad only ever goes on the other one. Buying a smart lock for French doors is mostly a question of which leaf gets it and what keeps the quiet one from swinging, and the spec sheet on the box answers neither.

The confusion is understandable. Hardware catalogs sell plenty of “French door” trim kits, but almost none of it is a lock built specifically for a double opening. What you are really shopping for is a standard smart deadbolt for the leaf that carries the hardware, plus a plan for the leaf that doesn’t.

That second part is the piece most buyers skip, and it is the one that decides whether the door actually closes square after the lock goes in.

Active and inactive: the term that decides everything

Door hardware catalogs call the two leaves active and inactive, and once you know the split, half the confusion about French door hardware disappears. The active leaf is the one with the working handle, the one you actually push or pull to get through the opening day to day. The inactive leaf stays closed behind it, held shut by its own hardware rather than by the lock on the active side, and it only gets opened on purpose, for moving furniture or letting more air through on a nice afternoon.

A smart deadbolt, a keypad lever or a full handleset goes on the active leaf and only the active leaf. Nobody makes a connected lock meant to span both doors of a pair, and trying to force one to do that job is how people end up with a bolt that will not throw because the two leaves have shifted half an inch out of alignment with each other.

What actually holds the inactive leaf shut

This is the part a spec sheet never covers, because it isn’t the smart lock’s job. The inactive leaf needs its own fixed point, and which one it gets depends on whether the opening is interior or exterior.

Interior French doors, one bore each

On an interior pair, the active leaf usually carries a privacy or passage lever, one bore, and the inactive leaf gets a matching non-turning dummy lever: same look, no mechanism inside, there purely so the two doors read as a set. A smart lock has no place on this side of the house in the first place, since there is nothing to connect to and nothing to protect.

Exterior French doors, a bolt the lock never touches

On an exterior pair this is where the smart lock question actually lives. The active leaf gets the deadbolt, and the inactive leaf is fixed in place by flush bolts: a slide bolt set into the top and bottom edge of the door, each one thrown by hand into a strike in the head jamb and the threshold. A plate with a small knob sits recessed into the door’s edge, barely wider than the door itself, which is why it goes unnoticed on doors that have had the same pair in place for years.

Those flush bolts carry real weight. The active leaf’s deadbolt only has to catch the strike on the inactive leaf, not the door frame itself, so a pair with a loose or half-thrown flush bolt on top effectively has no deadbolt security at all, smart or otherwise. Throwing both bolts fully, every time the inactive leaf gets closed, is the one habit that makes the rest of this article matter.

Where a smart lock for French doors actually goes

Schlage’s own guidance on French door hardware is reassuring on this point: any of its electronic and smart locks installs on a French or double entry door the same as it would on a single mechanical deadbolt, because the active leaf is prepped exactly like any other exterior door. What changes is the prep on the pair as a whole, and it comes in three common configurations.

• A single bore on the active leaf, no deadbolt bore cut at all. That is a drilling job before it is a shopping decision, and it is worth reading how a fresh bore gets cut before buying anything.
• Two bores on the active leaf, one for the entry handle and one for a deadbolt above it. This is the common case on a prepped exterior pair, and it is where a smart deadbolt drops straight in.
• Three bores, used when a full handleset covers both the deadbolt and the entry trim on the active leaf, with a matching dummy handle sometimes added to the inactive leaf purely for symmetry.
• Whatever configuration the active leaf already has decides the lock. The inactive leaf, flush bolts and all, is never part of the measurement.

If you have not settled on which category of keyless entry you actually want, the five distinct types sold as keyless entry is the earlier decision, and it applies to a French door active leaf exactly as it would to any other front door.

Single cylinder or double, and why it matters more here

A French door pair usually sits near a wall of glass, which is exactly the situation where a single cylinder deadbolt, keyed or keypad on the outside and a simple thumbturn on the inside, starts to look weak to a lot of homeowners. Someone could, in principle, break a pane and reach the thumbturn.

That is the reasoning that pushes people toward a double cylinder deadbolt, which needs a key on both faces and removes the thumbturn entirely. It is also the reasoning that a number of local codes restrict or ban outright on an exterior door, because a double cylinder lock can trap the people inside during a fire if nobody can find the key in the dark. A French door pair, with its own glass and its own flush-bolted second leaf, is precisely the kind of opening that fire officials have in mind when they write that rule. Check the local code before buying a double cylinder deadbolt for this opening, not after.

The handing question, twice

A single front door is handed once: hinges on the right or hinges on the left, decided by standing outside on the key side. A French door pair forces the same question twice, because the active leaf still swings one particular way even though its twin sits right beside it looking identical.

Deadbolts don’t care about handing, which is the main reason a smart deadbolt is the least complicated route onto the active leaf of a French pair. A keypad lever is usually reversible on the door in a few minutes. A full handleset is the one to check against the box before anything gets unpacked, because the thumb piece and interior lever are often cut for one direction only, and that handing trap applies just as much to a French door’s active leaf as it does to a single front door.

What the astragal can do to a retrofit lock

Many French door pairs meet in the middle over an astragal, a narrow strip fixed to the edge of the inactive leaf that the active leaf closes against, covering the gap between the two doors. It is a small piece of wood or metal, and it has an outsized effect on anything that clamps onto the inside of the door rather than replacing the cylinder outright.

A retrofit unit that clips over an existing thumbturn needs clearance to turn, and an astragal set close to the lock, or weatherstripping compressed tighter than it looks, can crowd that clearance more than it would on an ordinary single door. Measure with the door closed and the astragal in its normal position, not with the door standing open, because that is the one state a retrofit body actually has to operate in. The four measurements that decide whether a retrofit lock fits over an existing deadbolt cover this in more detail, and they are worth taking before ordering one for a French door’s active leaf specifically.

Common questions

Can I put a smart lock on French doors at all?

Yes, on the active leaf, installed the same way it would go on any other exterior door with a deadbolt bore. The inactive leaf keeps its flush bolts or its dummy hardware and never gets a lock of its own.

Which leaf of a French door pair gets the smart deadbolt?

The active leaf, the one with the working handle that gets used for everyday traffic. It is usually the leaf prepped with the deadbolt bore already, so there is rarely a choice to make.

Do I need to lock the inactive leaf separately?

It needs its flush bolts thrown, top and bottom, every time it is closed. That is a manual habit rather than a lock, and it is the step a loose-fitting pair usually fails on, since an unthrown flush bolt leaves the whole opening relying on a deadbolt that only catches the other door.

Will a retrofit clamp-on lock fit over my French door’s thumbturn?

Often, but check clearance against the astragal and the weatherstripping with the door closed before ordering. A model that clears easily on a single front door can bind on a French door’s active leaf if the astragal sits close to where the clamp needs to turn.

The short version

A smart lock for French doors is a standard smart deadbolt on the active leaf, nothing more exotic, and it installs the same way it would on any single exterior door with a deadbolt bore already cut. The inactive leaf is a separate problem entirely, held shut by flush bolts that need throwing by hand every time the door closes, not by anything connected to an app. Check local code before choosing a double cylinder deadbolt here, since the glass and the second leaf are exactly what egress rules are written around, and measure twice against the astragal before ordering a retrofit unit that clamps rather than replaces. Get the active leaf right and throw the flush bolts on the other one, and the pair behaves like any other well-prepped exterior door.