Last updated 2026-08-28
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Will a smart lock fit your door?
Most US doors take a standard deadbolt, and most smart locks are built for it. So the usual answer is yes. Returns come from the doors that sit slightly off that standard. You can find out which you have before you spend anything.
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The one decision that comes before any measurement
There are two kinds of smart lock and they solve different problems. A retrofit lock replaces only the thumbturn on the inside of the door and leaves your existing deadbolt, cylinder and keys alone. A full replacement swaps the whole deadbolt for a new one with a keypad on the outside.
Retrofit is the right answer far more often than its share of the market suggests. Nothing changes on the outside of the door, existing keys keep working, the landlord's lock is untouched, and reversing it is a screwdriver and five minutes. It also sidesteps three of the four measurements below, because the deadbolt that already fits stays where it is.
Full replacement is what you want if you need a keypad or a fingerprint reader on the outside, and it is the only option if the existing deadbolt is worn or you want to be rid of the keys entirely.
The four measurements, in the order that eliminates fastest
Door thickness
Measure the edge of the door. Standard US exterior doors are 1 3/4 inches and most locks cover a range around that, but thicker custom or solid doors go past it and need an extension kit that is often sold separately. This is the measurement that most often turns a purchase into a return, and it takes ten seconds.
Backset
From the edge of the door to the center of the round hole the deadbolt sits in. It is almost always 2 3/8 or 2 3/4 inches, and most full-replacement locks ship with an adjustable latch that does both. Worth confirming rather than assuming, because a lock without an adjustable latch will simply not reach.
Cross bore
The diameter of that round hole through the face of the door. The common size is 2 1/8 inches. An older or non-standard door with a smaller bore needs drilling out, which is a real job on a metal or fiberglass door and not a five-minute one.
Clearance around the thumbturn
This is the one nobody measures and the one that defeats retrofit locks. The housing is bigger than the thumbturn it replaces, so it needs clear space around it. A deadbolt set close to the door edge, a decorative escutcheon, deep trim, or a door that opens against a wall can all leave it fouling something. Hold a fist over the thumbturn; if that is tight, so is the lock.
A lock is not a door, and a door is only as good as its frame
A smart lock changes how the bolt is operated. It does not change how strong the door, the frame or the strike plate are, and on most houses the frame gives before the lock does. If you are upgrading for security rather than for convenience, longer strike screws into the framing timber cost very little and address the part that gives way first.
Retrofit
Yale Approach retrofit smart lock
Replaces the thumbturn on the inside of the door and leaves the deadbolt, the cylinder and your keys exactly as they are. Nothing changes on the outside, which is what makes it the workable option in a rental and on an off-center or non-standard bore. Measure the clear space around the existing thumbturn before ordering, because that is the one thing it does need.
Full replacement
Schlage Encode smart Wi-Fi deadbolt, Camelot trim
A full-replacement deadbolt with a keypad on the outside, for when you actually want to stop carrying a key. This is the type that cares about measurements. Check yours with a tape first: door thickness 1 3/8 to 1 3/4 inches, backset 2 3/8 or 2 3/4 inches. No hardwiring, but consider whether a storm door will still close over the escutcheon.
Retrofit
Philips Wi-Fi smart retrofit lock
The same retrofit idea from a second maker. Thumbturn housings differ in size, and the one that clears your trim may not be the first you try. Built-in Wi-Fi, so it wants a usable signal at the door.
The awkward doors, and what actually happens on them
- Apartment doors with a mortise lock. The lock body sits inside a pocket in the door edge instead of a round bore. Consumer smart deadbolts do not fit these, and the answer is usually a retrofit unit if the interior thumbturn is standard, or nothing.
- Off-center or non-standard deadbolts. Common in older houses and in anything fitted by hand. Retrofit is the escape route, because it does not care where the bore sits as long as there is room around the thumbturn.
- A storm door in front. Measure the gap. A keypad escutcheon adds depth to the outside of the door and can stop a storm door closing.
- Double doors and narrow stiles. A narrow stile may not have the width for a standard bore at all, and this is where it stops being a shopping problem and starts being a joinery one.
Questions people ask
Usually a retrofit lock, yes, because nothing on the outside of the door changes and the original hardware goes back in minutes. Ask anyway, in writing, and keep the parts you removed. The lease page covers the same ground for the doorbell.
With a retrofit lock, yes, because the cylinder is untouched. With a full replacement, no, unless you have it rekeyed to your existing key, which a locksmith can often do.
Nearly every one takes a physical key or has an external contact you can jump from a battery. Check which before buying, and check it before you need it, because reading the manual on a doorstep in the dark is the worst version of finding out.
Some connect over Wi-Fi, some over Bluetooth to your phone, some through a separate bridge. If your front door already has a weak signal, that is worth settling before you choose, and it is the same problem the doorbell has.
Measured, and it fits
The lock is one half of this. The door and the frame it hangs in are the other.
- Can renters install one: the same permission questions apply to a lock
- The five-minute check before you install: free checks worth doing before any box is opened
Related
- Wi-Fi will not reach the front door (the same weak spot affects both)
- Can renters install a doorbell camera? (lease wording, and what reverses cleanly)