Holds a real key behind a code so visitors get in without carrying anything of yours.
also: key safe, lockbox, key vault
The basics
What to know about smart locks
A motor bolted to a deadbolt
A smart lock is an electric motor, a battery pack and a small radio bolted onto an ordinary mechanical lock. The mechanical part still does every bit of the security work, because what stops a door is a steel bolt crossing into the frame. Electronics only decide when that bolt moves and who is allowed to move it. Five shapes cover nearly everything sold: a smart deadbolt that replaces the whole lock, a retrofit adapter that drives the thumbturn you already own, a keypad deadbolt with no phone connection at all, a smart lever handle that holds a spring latch rather than a bolt, and a key lock box that stores a physical key behind a code.
What happens inside the housing
Inside the interior housing, a geared motor turns the same cam your thumb used to turn. It draws power for the one or two seconds the bolt is moving and almost nothing in between. That means four AA cells usually run 6 to 12 months at about eight cycles a day. Radios rewrite that arithmetic. Bluetooth Low Energy, a short range radio designed for battery devices, reaches roughly 30 feet and speaks only to a phone standing near the door. Wi-Fi built into the lock lets you open it from another country and can drop battery life to 2 to 4 months. A bridge, meaning a small plug-in box that talks Bluetooth to the lock and Wi-Fi to your router, buys the same remote access while leaving the batteries alone. Z-Wave and Zigbee are low power mesh radios that need a hub and hop through mains-powered devices, covering 30 to 50 feet per hop. Thread behaves the same way and needs a Thread border router, a device that joins that mesh to your network. Matter is the shared standard that lets different makers cooperate, not a radio of its own.
Getting in, and staying connected
Getting in is a separate question from how the lock talks. A keypad takes a 4 to 8 digit code, works when your phone is dead, and hands each person a number you can delete later, which beats a key you can never take back. Fingerprint readers open in under a second and miss on wet, cold or worn fingertips, so keep a code behind one. Auto-unlock reads your phone's location and opens the door as you walk up. It is the flakiest feature on the product, since your phone must notice you left a radius of a few hundred feet and then return, so it fires early, late or never.
Renting, and the landlord's key
Renters gain most from a retrofit adapter, because the outside cylinder and the landlord's key stay exactly as they were and the original thumbturn goes back in a drawer. Families whose children keep losing keys want a keypad and codes that expire. If you host short stays or send in cleaners, the log and scheduled codes matter more than the metal. You can see that the afternoon code was used at 2:12 and switch it off on Sunday. Gates, sheds and site containers take a smart padlock. Doors in much of Europe, Australia and Asia use a mortise lock inside a narrow stile. So a North American deadbolt will not fit them.
The part sellers skip
Now the part sellers skip. Your lock is only as strong as the door, the frame and the strike plate, and a smart one fixes none of those. Almost every forced entry breaks the jamb, not the bolt. The usual reason is a strike plate held by 3/4 inch screws that bite only soft trim. Swap them for 3 inch screws reaching the framing behind and you have improved your security more than any electronics will. Batteries add a failure mode a key never had, keypads wear so the used digits shine, and a lock tied to a cloud account inherits every risk of that account. Escape rules matter too. Many places require you to open the door from inside without a key, which rules out some keyless and double-cylinder setups, and codes vary by country and city, so check yours.
Look for an ANSI grade
Judge candidates on five things. Look for an ANSI/BHMA grade, the North American durability and force standard, where Grade 1 is strongest and Grade 3 is weakest; Grade 2 suits most homes and Grade 3 belongs on an interior door. Confirm a 1 inch bolt throw, since a shallow bolt pops out of a spread frame. Ask what happens at zero battery, whether that is a keyway, exterior contacts for a 9V battery or a USB-C port, and learn that answer before you need it. Find the security update window in writing and treat anything under five years as short. Insist on two-step sign-in, and prefer a lock that still opens by code and by phone at the door when your internet is down.
Change batteries on a date
Upkeep is short but unforgiving. Change batteries on a date rather than on the low warning, use lithium AA cells where winter drops below freezing, and never mix brands or ages. Twice a year, shut the door and throw the bolt by hand: if you have to lift or lean on the door, the frame has moved and the motor will stall trying. Rotate keypad codes yearly and wipe the keys, because four worn digits cut a 10,000 code range down to 24 guesses. Install firmware only with fresh cells, and prune old codes and app users the way you would prune old keys.
Buyer checklist
Before you buy smart locks
Electronics combine hardware, software and services. Compatibility and support life matter as much as the headline specification.
01
Map the whole setup
Confirm the ports, operating system, network, accessories, apps and services the product must work with.
02
Check the support period
Look for a clear security and software-update policy, especially on connected products and discounted older models.
03
Separate included from subscription
Find out which recording, storage, analytics, content or remote features need an ongoing payment.
04
Plan for repair and data
Check battery and spare-part service, warranty handling, account controls and how personal data can be exported or deleted.
Measure the backset before anything else: the distance from the door edge to the center of the bolt hole is either 2-3/8 inches (60 mm) or 2-3/4 inches (70 mm). Most deadbolts switch between the two, a few ship fixed at one, and a 3/8 inch error leaves the bolt hitting the strike plate instead of the hole.
Check the door thickness with a tape. Standard doors run 1-3/8 to 1-3/4 inches (35 to 44 mm), which almost every lock covers. Solid timber and insulated entry doors often exceed that and need a longer spindle and screws, so order the extension kit by your measurement rather than assuming one is in the box.
For a retrofit adapter, measure the space around your thumbturn: you want a clear circle of 2-1/2 to 3 inches and 2 to 2-1/2 inches of depth behind the door face. A security chain, a door frame, an inward-swinging storm door or a decorative plate inside that circle rules it out, and so does a key on both sides.
Test the strike before you spend anything. Close the door and throw the existing bolt by hand. If you have to lift, push or lean on the door to make it go, a motor will stall in the same spot and empty a set of cells within weeks. Correct the alignment first, then shop.
Site a bridge or hub within 20 to 30 feet of the lock with no more than one wall between them. Bluetooth from a lock is deliberately weak to protect the batteries. A bridge two rooms away turns into a device that reports itself unavailable every third try.
Look at what the door faces. In a cold climate ask for a stated operating range down to at least -4 F (-20 C) plus a weather rating for the exterior half. A dark west-facing door in a hot climate can reach 140 F (60 C) at the surface, which shortens battery life and can wash out a screen.
Care
Caring for smart locks
Change the batteries on a calendar rather than on the warning: once a year for a Bluetooth, Z-Wave, Zigbee or Thread lock, twice for one with Wi-Fi inside. Fit four fresh cells of one brand together, because a pack runs down to its weakest cell and a single half-used AA drags the rest with it.
Switch to lithium AA cells if your winter drops below freezing. Alkaline cells give up roughly half their usable capacity at 0 F (-18 C). This is exactly why locks quit during the coldest week of the year rather than spreading the failures out.
Shut the door and throw the bolt by hand every spring and fall. Timber frames move about 1/16 inch with humidity. That much is enough for the motor to grind, report the door as locked and leave the bolt sitting short of the strike.
Put 3 inch screws through the strike plate and the top hinge so they reach the framing behind the jamb. The 3/4 inch screws supplied with most hardware hold only the soft trim. This one change resists a kick better than any upgrade inside the lock.
Wipe the keypad monthly and rotate every code once a year, plus immediately after any contractor visit. Skin grease and wear pick out the four digits you use, and knowing which four cuts a range of 10,000 codes down to 24 orders worth trying.
Lubricate the cylinder with dry graphite or PTFE and keep oil away from it, since oil holds grit and gums the pins until the motor strains. Run firmware updates only on fresh cells, because power lost part way through a write can leave the lock unresponsive.
Questions
Common questions
What actually happens when the batteries die?
You get 2 to 4 weeks of warning first, then nothing. Most locks keep a keyway, so one spare key in a wallet or a car ends the problem. Keyless models offer exterior contacts for a 9V battery or a USB-C port that runs from a power bank. Work out which of those three you have before it happens rather than after.
Can someone hack a smart lock open?
Far less likely than the door being kicked. Radio attacks need proximity, skill and a target worth the effort; a strike plate held by 3/4 inch screws needs a boot. Your account is the softer target, so switch on two-step sign-in, use a password you use nowhere else, and delete app users when people move out.
How long do the batteries really last?
Six to twelve months on four AA cells for a Bluetooth, Z-Wave, Zigbee or Thread lock at roughly eight cycles a day. Built-in Wi-Fi drops that to 2 to 4 months, because the radio has to stay reachable. A stiff bolt, a misaligned strike or a hard freeze can halve any of those numbers.
Will it still work if my internet goes down?
The lock keeps working. Codes, keys and a phone standing at the door over Bluetooth all still open it, while remote locking, notifications and any hub routine that runs through a cloud service stop. Ask whether guest codes live in the lock or are fetched online, since a few designs fetch them and lock out your visitor.
Can I fit one myself?
Yes for a deadbolt swap: 20 to 40 minutes, one Phillips screwdriver, and no drilling when the door already has standard prep. A retrofit adapter takes about 10 minutes. The exceptions are hardwired locks and electric strikes, which need mains power or a transformer. That counts as licensed electrical work in most places.
My landlord will not let me change the lock. Any options?
Ask in writing first, then fit a retrofit adapter. It clamps over your interior thumbturn, so the outside face, the cylinder and the landlord's key stay exactly as they are. The whole thing comes off in ten minutes when you leave. Keep the original thumbturn and its screws somewhere safe, because that is the part people lose.
Is a smart lock as strong as a plain deadbolt?
Identical, when the grade and the bolt match. Both are steel, and a Grade 2 deadbolt with a 1 inch throw resists the same force whether a motor or your thumb turns it. Electronics change who can open the door, not how hard it is to break. In nearly every real break-in the frame gives way, not the lock.
Can I still get out in a fire?
You must be able to, and building codes in many countries require an interior door to open without a key or a code. Keep a thumbturn or lever inside that always works, whatever the batteries are doing. Double-cylinder deadbolts with a key on both sides are restricted or banned in some places, and rules vary by country and city, so check yours.
