Installing a Smart Lock on a Door That Never Latched Right

Why this matters

A motorized smart lock has a small motor and a strict idea of what "locked" means: the bolt has to travel its full throw in a set time without stalling. A door that the owner has always locked by lifting the knob, leaning on it, or giving the thumb-turn an extra shove will defeat that motor within a week. The lock reports "jammed", eats batteries, or worst, tells the app it is locked when the bolt stopped halfway. The customer blames the lock and the installer. Fixing the door first is not extra work; it is the install.

Before you start: what can hurt someone

• Lockout and egress. Before removing the existing deadbolt, confirm someone in the house has another way in and out and that a physical key or keypad code will work before you leave. The egress door must stay openable from the inside without a key or special knowledge; the IRC states that at R311.2, as adopted (often with amendments) by your jurisdiction. Never fit a double-cylinder or a key-to-exit configuration on it.
• Driving long screws into the hinge jamb. Before a 3 in screw goes into the framing, look for an alarm door contact, doorbell wire or a cable run in the jamb, and keep the screw clear of it.
• Chiseling a painted jamb. In a house built before 1978, assume the paint on the jamb and stop may contain lead, the condition EPA's renovation rule at 40 CFR 745 is written around. Enlarging a strike mortise is small work, but chiseling dry paint makes lead dust: mist it, catch the chips on plastic, clean with a HEPA vacuum, and never sand it dry.
• Drilling. Eye protection on for every bore into the jamb or the door edge.
• Lifting the door. If you have to take the door off its hinges, an exterior slab is two people.

The procedure, in the order the door depends on

The order is not a preference. Every later step depends on the earlier one being right, so a strike moved before the hinges are fixed is a strike you will move twice. Each step below carries what you do, why, and what happened on one real job: a front door on a twenty-year-old house where the owner had always lifted the handle to lock, and where a smart lock installed by the homeowner reported "jammed" on roughly one lock in three.

1. Watch it fail before you touch anything. With the door closed, try to throw the existing deadbolt by the thumb-turn, gently. Note whether you have to lift, push or pull the door to make it go. Then open the door and throw the bolt in free air. Reason: a bolt that is smooth in free air and stiff with the door closed is a door problem, not a lock problem. Skipping this sends you straight to the lock, which is the one part that is usually fine.

On the job: the bolt threw easily with the door open. With the door closed, it stopped about halfway unless the handle was lifted.

2. Read the reveal. The reveal is the gap between the door and the jamb. Look at it on the latch side, top and bottom, and along the head. A healthy door has a roughly even gap all round, commonly about 1/8 in. A door that has sagged shows a tight gap at the top latch corner, a wide one at the bottom latch corner, and a wide gap at the top of the hinge side. Reason: the reveal tells you which way the door has moved, and the strike has to follow the door, not the other way round.

On the job: top latch-side gap about 1/32 in, bottom latch-side gap about 3/16 in, and the hinge-side gap opened toward the top. Classic sag: the top hinge had pulled away from the framing.

3. Fix the hinges first. Tighten every hinge screw. On the top hinge, replace one or two of the short jamb-leaf screws with 3 in screws that reach through the jamb into the framing behind it, which pulls the top of the door back toward the hinge side and lifts the latch corner. Snug them; over-driving can bow the jamb. Then re-read the reveal. Reason: short jamb screws only grip the thin jamb, which is why the door sagged. If you align the strike to a sagging door, it will keep sagging, and the strike will be wrong again by next season.

On the job: two 3 in screws in the top hinge. The reveal came back to about 1/8 in at both latch corners.

4. Mark the strike and read the mark. Rub lipstick or dry-erase marker on the end of the deadbolt, close the door, and try to throw the bolt so its tip touches the strike. Open the door and read where the mark landed relative to the strike opening:

 STRIKE PLATE, seen from the hallway side
 (stop side is toward the right)
 +--------------------------------+
 |  A  mark above the opening     |
 |   +------------------------+   |
 | C |    strike opening      | D |
 |   +------------------------+   |
 |  B  mark below the opening     |
 +--------------------------------+
 A  door has risen or strike sits low
 B  door has dropped: back to step 3
 C  door stands off the stop: you push
    the door to lock it
 D  bolt rides the stop side: strike
    sits too far toward the stop

A mark at B means the hinge fix is not finished, and you go back to step 3 before touching the strike. A mark at A or at C or D, with an even reveal, means the strike moves. Reason: the mark shows where the bolt actually meets the jamb, which is information the reveal cannot give you to the nearest 1/16 in.

On the job: before the hinge fix the mark sat about 1/8 in below the opening, position B. After the hinge fix it sat inside the opening but touching its bottom edge. A light file on the bottom edge of the opening, and a matching paring of the wood behind it, gave clearance.

5. Give the bolt its full throw. Most residential deadbolts throw about 1 in; read the lock's sheet. The hole behind the strike has to be deeper than that throw, and many lock sheets ask for about 1/4 in of extra depth. Push a pencil into the hole, mark the depth, and measure. Reason: a motorized lock decides it is locked when the bolt reaches full extension. A bolt that bottoms out in a shallow hole makes the motor stall at the end of travel and the lock calls that a jam, even on a perfectly aligned door.

On the job: the hole behind the strike measured 3/4 in deep, a quarter inch short of the throw, left that way by the original installer. It was drilled out with a 1 in spade bit to about 1-1/4 in, with eye protection on.

6. Run the two-finger test. With the door closed and the old deadbolt (or the new lock's mechanism with its motor disengaged, if the sheet allows) in place, the bolt must throw fully, to the stop, with two fingers on the thumb-turn and no pressure on the door. Repeat with the weatherstripping compressed as it will be in winter: pull the door closed firmly and try again. Reason: this is the test the motor will run hundreds of times a month. If your fingers need to work, the motor will stall.

On the job: full throw with two fingers, door closed, on five tries, including with the door pulled hard against the weatherstrip.

7. Install the lock to its sheet. Now, and only now, fit the smart lock: bolt orientation, the tailpiece or spindle seated into the mechanism, the interior unit square to the door. Most motorized locks then run a calibration that learns where the bolt stops; run it with the door closed. Reason: calibration on a binding door teaches the lock the wrong end of travel, so even after the door is fixed it will keep reporting a fault until it is re-calibrated.

8. Cycle-test from every input before you leave. Lock and unlock ten times from the app, then at least three times each from the keypad, the physical key and the thumb-turn by hand, all with the door closed. Watch for a cycle that runs longer than the others or a status that disagrees with what you can see. Reason: one good cycle proves nothing; a lock that jams one time in three passes a single test two times in three.

On the job: ten app cycles, three keypad, three key, three by hand. Every lock cycle completed with the same short motor sound and the app reported locked each time. Against the homeowner's original install, which jammed on about one lock in three, the change was the door, not the lock.

What changes the answer

• The door swells seasonally. A wood door that binds only in humid months needs its edge planed and sealed, not a strike moved. A strike set to the swollen door rattles all winter.
• The frame itself is out of square. If the reveal is uneven in a way that hinge screws cannot correct (a header that has dropped, a jamb that has twisted), the door needs re-hanging or the frame needs work. That is carpentry beyond a lock install; price it separately and say so before you start.
• The door is a storm-door pair or has a deep stop. Some locks need clearance the door cannot give. Read the lock's sheet for minimum door thickness and backset (commonly 2-3/8 or 2-3/4 in) before you sell the lock, not after.

When it still jams with the door fixed

If the two-finger test passes and the motor still stalls, the fault has moved inside the lock, and three causes account for most of it.

• Batteries. A motor's torque falls with its supply voltage, so a lock that worked on fresh cells and starts jamming weeks later on a marginal door is telling you the door is still slightly tight. Check what battery chemistry the lock's sheet calls for; some state that rechargeable cells, which run at a lower voltage per cell, will under-report charge and lose torque early.
• The tailpiece is clocked wrong. The flat bar that connects the exterior cylinder to the interior motor unit must sit in the orientation the sheet shows. Off by a quarter turn, the motor drives the bolt against its own end stop before it reaches full throw.
• The interior unit is not square. Mounting screws drawn tight against a door face that is not flat can cock the motor housing and add friction to every turn. Back them off a quarter turn and re-cycle.

And the lock says locked when it is not. Some locks infer "locked" from the motor's travel, others from a separate door-position sensor. A lock with a misplaced door-position magnet can report locked with the door ajar. Shut the door, lock from the app, then try the handle from outside before you trust the status.

How you know it is right

• Even reveal, about 1/8 in, at both latch-side corners.
• A strike mark centered inside the opening, not touching an edge.
• Full throw with two fingers on the thumb-turn, door closed, weatherstrip compressed.
• Ten consecutive motor cycles with no jam and a status that matches the bolt.
• The job record names what you changed on the door (hinge screws, strike filed, hole depth), so if the lock reports a jam next year the next tech checks the door first.

References

• International Residential Code R311.2 on egress door operation, as adopted by your jurisdiction
• Smart lock and deadbolt manufacturer documentation for throw, bore depth, backset and calibration
• EPA Renovation, Repair and Painting Rule, 40 CFR 745 Subpart E, for disturbing paint in pre-1978 homes
• See related: Who Owns the App Account on a Connected Device; Leaving a Device Record the Next Tech Can Use