How to Install a Smart Lock: Full Replacement and Retrofit

How do you install a smart lock?

A full deadbolt replacement is four screws out, four screws in, and about thirty minutes with a Phillips screwdriver. A retrofit is closer to ten. Both need one step almost every guide omits: check and correct strike alignment first, because a misaligned strike is what makes a new lock jam.

Tools

Almost nothing. A #2 Phillips screwdriver does the entire job on both install types, and a manual driver is better than a power one because it is much harder to overtighten and crack an escutcheon. Add a tape measure for the fit check, a pencil for marking strike positions, and 3 in wood screws for the strike plate upgrade described below. If the strike needs adjusting you will also want a sharp 1/2 in chisel and, for a shallow pocket, a drill with a 1 in spade bit.

What you do not need for a standard install: a drill for the lock itself, a hole saw, or a jig. If the instructions for your model call for drilling the door, you are either fitting a lock to an undrilled slab or fitting one that does not match your bore, and both are a different job.

Part A: replacing a full deadbolt

1. Unpack and sort. Lay out the exterior escutcheon, interior escutcheon, bolt assembly, strike plate, screws and battery pack. Find the printed manual and keep it open. Do not install batteries yet.
2. Remove the old interior escutcheon. Two screws, usually vertical. The interior half lifts away and the exterior half comes off with it or immediately after.
3. Remove the old bolt. Two screws in the faceplate on the door edge. Slide the bolt assembly out of the edge bore. Keep every original part in a bag; if you rent, you are reinstalling all of it later.
4. Clean the bores. Wipe out sawdust and old grease. If paint has built up in the edge-bore mortise, pare it back to clean wood with a chisel now, while there is nothing in the way.
5. Set the backset on the new bolt. This is the step that gets skipped. The new bolt assembly is adjustable between 2-3/8 in and 2-3/4 in; the manual shows which position is which, usually a collar you extend or a cam you rotate. Set it to match the number you measured, then slide it into the edge bore.
6. Check bolt orientation.The bolt has an up. Most have an arrow or the word TOP stamped on the assembly, and the tailpiece slot must be horizontal (or whatever the manual specifies) when the bolt is retracted. Getting this wrong means the lock reads “locked” when the bolt is out and “unlocked” when it is in.
7. Fix the faceplate. Two screws, snug not tight. The faceplate should sit flush with the door edge, not proud. If it stands proud, the mortise is too shallow and needs a few passes with a chisel.
8. Fit the exterior half. Feed the cable (on locks with a keypad outside) and the tailpiece through the cross-bore and hold the exterior escutcheon square against the door. On most models a small mounting plate goes on the inside first.
9. Fit the interior half. Route the cable so it is not pinched between the escutcheon and the door — a pinched ribbon cable is a common cause of a keypad that works for a week. Engage the tailpiece into the interior mechanism, then start both through-bolts by hand before tightening either.
10. Tighten evenly, alternating. Snug one, then the other, then back to the first. Overtightening one side skews the mechanism and causes binding.
11. Test by hand, door open. Batteries still out. Turn the thumbturn and watch the bolt extend and retract. It must move freely with no resistance. If it does not, something is misaligned inside and no amount of motor will fix it.
12. Deal with the strike. Do this before batteries. Part C below.
13. Batteries, then calibration. Fit the cells, then run whatever calibration or auto-alignment routine the manual describes. Most locks learn the travel of your specific bolt during this, which is why doing it before the strike is correct produces a lock that has learned a bad door.
14. Set up codes and the app last.Change the default master code. Enroll a code for every household member rather than sharing one, so a departure means deleting one code rather than changing everybody's.

Part B: fitting a retrofit

A retrofit lock — the August Wi-Fi Smart Lock, the SwitchBot Lock Pro, the Yale Approach — replaces nothing. It mounts to the inside face of the door over your existing thumbturn and turns it with a motor. The exterior of the door and your keys are untouched, which is why these are the answer for rented doors and for doors whose measurements came back non-standard. The full field is in our no-drilling roundup.

1. Test the existing deadbolt by hand first.Not optional. Open the door, turn the thumbturn, and feel the resistance. Then close the door and turn it again. If the closed-door turn is noticeably harder, stop and fix the strike (Part C). A retrofit motor inherits every mechanical problem the bolt already has — the SwitchBot Lock Pro's own guidance says a stiff deadbolt will jam it, drain the battery and report failures.
2. Check clearance. Hold the unit against the thumbturn and confirm it does not foul the door edge, the architrave, a narrow stile, or a storm door behind the opening. Retrofit bodies are bulky and this is the most common physical failure.
3. Fit the mounting plate. Most kits offer two routes: adhesive, or replacing the two interior escutcheon screws with the supplied longer ones. The screw route is more reliable and just as reversible — you are reusing existing holes, not drilling. Use adhesive only if the interior plate geometry rules out the screws.
4. Fit the thumbturn adapter.Kits ship several sizes to grip different thumbturn shapes. Choose the one that grips with no slop at all; a loose adapter is what produces “it turns but the bolt does not move.”
5. Mount the body and calibrate.Clip the unit onto the plate and run the app's calibration, which teaches it the locked and unlocked positions of your specific thumbturn. Do this with the door closed, so it learns the real travel.
6. Cycle it ten times. Lock and unlock repeatedly and listen. A consistent sound each cycle is what you want. Any cycle that sounds like it is straining means the underlying bolt is fighting the strike.
7. Add the hub or keypad if you bought one.Remote access on a Bluetooth retrofit needs the manufacturer's hub; code entry needs their keypad. Both are separate purchases and both are hardware, not subscriptions.

Part C: strike alignment — the step everyone skips

If you read one section of this page, read this one. The overwhelming majority of “my smart lock jams,” “the motor grinds,” and “it eats batteries” complaints are a strike plate that is a few millimeters out of position. A human hand compensates for that without noticing, by lifting the handle or leaning on the door. A motor cannot lean on anything. It just pushes until it stalls, logs a failure, and tries again.

Diagnosing it

1. Door open, throw the bolt by hand. It should extend its full travel — about 1 in on a residential deadbolt — with light, even resistance.
2. Door closed, throw it again. Any additional resistance is misalignment. If you have to lift, push or pull the door to get it to throw, the strike is wrong.
3. Find out which way. Color the tip and sides of the bolt with a pencil or a marker, close the door, and throw the bolt until it stops. Open up and look at the strike plate: the mark shows exactly where the bolt is hitting — high, low, or on the near edge.
4. Check the pocket depth. Poke a pencil into the hole behind the strike plate. The bolt needs at least a full 1 in of clear depth. Builders routinely leave a shallow pocket, and paint fills what is left.

Correcting it

If the bolt is hitting the plate high or low, the usual cause is hinge sag and the usual fix is at the hinges rather than the strike: replace the middle screw of the top hinge with a 3 in screw that reaches the framing, and drive it home. This pulls the top of the door back toward the hinge jamb and lifts the latch edge, often by exactly the amount needed.

If the bolt is hitting the near edge of the plate, the door is not closing far enough, usually because of compressed or overthick weatherstripping. Adjust the stop or the weatherstrip rather than moving the strike.

If the plate itself is in the wrong place, remove it, enlarge the pocket in the needed direction with a chisel, plug the old screw holes with glued dowel or matchsticks so new screws bite into solid material, and refit. Never rely on screws re-driven into their own worn holes; they will drift back.

The 3 in screw upgrade

While the strike plate is off, replace its screws with 3 in wood screws that pass through the jamb and into the framing stud behind it, and fit a strike box if the kit includes one. This costs a few dollars and does two useful things at once: it anchors the strike into structure rather than into a strip of trim, and it holds alignment as the frame moves with the seasons. It is the single highest-value change you can make to any door, and it is described in more detail in our threat model guide.

“It jams intermittently” — what that almost always means

Intermittent is the diagnostic clue. A lock that fails consistently is misassembled. A lock that fails sometimes is fighting something that changes, and in a door only a few things change.

• Seasonal movement. Wood doors and frames swell in humidity and shrink in dry cold. A strike that is marginal in July is out of tolerance in January. If your lock became unreliable at a change of season, this is the answer, and the fix is realignment plus long screws, not a new lock.
• Falling battery voltage. Motors lose torque as cells deplete long before the app reports a low battery. A lock that has been fine for six months and now fails one cycle in five is telling you the battery reserve no longer covers a marginal strike. Fresh cells will mask it for a while; the strike is still wrong.
• Hinge sag. Progressive rather than seasonal. The bolt starts hitting slightly lower on the plate over months. The top-hinge long-screw fix addresses it.
• Door not fully closed. On doors with stiff weatherstripping the door can rest a couple of millimeters proud unless pushed. Auto-lock then fires against a bolt that cannot reach its pocket. A door position sensor is a cheap way to know this is happening rather than guessing; the door and window sensors we cover report open, closed and left-ajar states.
• A retrofit adapter that has loosened. On retrofits only: re-seat the thumbturn adapter and re-run calibration.

Notice what is not on that list: the motor. Motor failure in these locks is rare, and almost every unit returned as faulty was fighting a door. Correcting the strike takes twenty minutes and is the difference between a lock that works for five years and one that gets returned in three months.

If you are still choosing hardware, the best smart locks roundupranks the field and states each pick's install type, and our methodology explains how those judgments were compiled from manufacturer manuals rather than from a bench. More explainers are on the guides hub.