Will a smart lock fit the door I already have?
Usually, if that door already wears a deadbolt. Two numbers decide it. The bore is the round hole punched through the face of the door, almost always 2-1/8 inches across on residential hardware. The backset is the distance from the edge of the door to the center of that hole, and it comes in two common sizes: 2-3/8 inches or 2-3/4 inches. Retail locks are built for those numbers and adjust between the two backsets.
Door thickness is the third number, and the one people forget. Standard exterior doors run 1-3/8 to 1-3/4 inches, and the screws packed in the box are cut for that span. A thicker custom slab or a door someone built up with a storm panel needs longer hardware, which is a parts problem rather than a fit problem.
Smart locks bring one more thing to check that a plain deadbolt does not, which is room on the inside face. The interior half carries a motor and a battery pack, so it is taller and deeper than the thumbturn it replaces. On a door with a narrow stile, or with the deadbolt set close under a window light, that housing can end up overlapping trim or glass. Worth a look before you buy.
How do you measure a bore and a backset?
You need a tape measure and about two minutes with the door open.
- Measure across the round hole in the face of the door. Take out the old lock first if you want a clean read, though you can usually measure the trim ring instead and subtract a hair.
- Put the end of the tape on the edge of the door and read to the center of that hole. That is your backset. Anything within a sixteenth of 2-3/8 or 2-3/4 counts as standard.
- Measure the thickness of the door at its edge.
- Look at the hole in the edge where the bolt slides through. One inch is the normal size there.
Then photograph three things: the inside face of the door around the lock, the door edge with the bolt out, and the frame where the bolt lands. Those photos answer more questions on a phone call than any description does.
What about older doors and manufactured-home doors?
Two door types on the mountain fall outside the standard numbers often enough to check first. Solid doors on Albertville’s older brick ranches were sometimes bored by hand, so the backset measures between the two standards or the bolt hole sits a little high. Manufactured and mobile-home entry doors are the bigger break: many use a thin metal skin over a narrow frame, with a keyed knob and deadbolt combined into one flat plate rather than two separate bores.
That combination unit is its own hardware category. A retail deadbolt will not fit its cutout and a smart deadbolt certainly will not, so the honest options are a replacement unit made for that opening or a keyless deadbolt added elsewhere on the door where the frame can carry it. Anyone who tells you a standard lock drops into a mobile-home door has not measured it.
Doors that never had a deadbolt are a separate job again. Boring a new hole through the face and the edge, chiseling the strike into the jamb, and lining the two up is real work with a jig, and it is the job that most often gets done crooked by a weekend drill.
My new deadbolt is stiff. Is the lock defective?
Usually it is not. The bolt is fighting the strike. A door settles, the jamb takes up humidity through an Alabama summer, hinge screws back out a turn or two, and the hole in the frame drifts a quarter inch out of line with the bolt. Brand new hardware feels exactly as bad on that door as the lock you took off, because the misalignment lives in the frame.
You can spot it in ten seconds. Close the door and throw the bolt. If it turns with two fingers, the alignment is fine. If you are leaning a hip into the door or lifting the knob to get the bolt home, the strike is off. Look for a bright scrape mark inside the strike plate, which is the bolt telling you which way it wants to move.
Smart locks are less forgiving about this than a thumbturn is. Your wrist can muscle a bolt through a tight strike without noticing. A small motor cannot. It stalls, retries, burns through batteries, and reports the door as locked when the bolt only made it halfway. Plenty of smart locks get blamed and returned over a strike plate that was a quarter inch off. Fixing alignment means moving the strike plate, sometimes deepening the mortise, and running screws long enough to reach the stud behind the jamb. That part is deadbolt installation and lock repair work, and it takes minutes when the tools are already out.
Can you keep the keyed lock you have?
Often, yes, and it is the cheapest good outcome on the door. Plenty of smart deadbolts keep a real keyway for the times the batteries die, and a lot of homes only want the keypad on one door anyway. Whatever keyed cylinders stay on the house should be rekeyed to a single new key while a locksmith is standing there, which runs $20 to $35 per cylinder. Otherwise you finish the upgrade holding a keypad code plus three mismatched keys.
If you are weighing keeping hardware against buying new across the whole house, the rekey-or-replace guide walks through that decision by situation.
Does a storm door change anything?
It can, in two ways worth knowing before the box is open. Clearance is the first: the exterior half of a smart lock stands proud of the door, and on a tight storm door installation the closer arm or the lower frame rail passes right through that space. Measure the gap between the two doors when the storm door is shut, and remember a keypad needs a hand in front of it.
The second is the double-lock habit. A storm door with its own key lock plus a deadbolt behind it means two locks, two keys, and one of them is a small cylinder nobody has rekeyed since the house was built. Homeowners who go keyless on the entry door frequently forget the storm door still takes a key, and a gust off the mountain shuts it behind them, which is a tedious way to get locked out of your own house. If you are upgrading, decide what the storm door is for. A latch keeps it from blowing. A key lock on it adds almost nothing to a house that has a real deadbolt behind it.
What does installation cost next to the box price?
The price board lists deadbolt install (new bore) at $90 to $180, with hardware included at the mid range and premium brands quoted up front. Rekeying is $20 to $35 per cylinder. A smart lock you bought yourself is labor rather than hardware: the swap, the strike alignment, the test cycles, and the pairing, quoted on the phone once we have your measurements and photos.
Set that against the shelf price of the lock and it reads about right. The box holds a part. Whether that part still works next July comes down to the fit and to a strike plate screwed into the stud behind the jamb, and none of that is in the box.
Buy first, or call first?
Call first if the door is older than you are, if it is a manufactured home, if there is no deadbolt on it yet, or if any of your measurements landed between the standard numbers. Two minutes on the phone beats a return trip to the store.
Buy first if you have a standard bored door, a lock you already like, and a clean 2-3/8 or 2-3/4 backset. Hang onto the box and the receipt until the bolt has thrown twenty times cleanly on a closed door, which is the test that catches a strike problem before the return window shuts.
