Does a smart lock replace the whole deadbolt?

It depends on the design, and this is the single biggest buying decision. A full-replacement smart lock swaps both the interior thumbturn and the exterior cylinder, so you get a keypad outside and usually a new key. A retrofit model, such as the interior-only designs, clamps over the thumbturn of the deadbolt you already own and turns it with a motor — your existing keys and exterior hardware stay exactly as they are. Renters almost always want the retrofit type, because the door is never drilled and the original hardware is never removed.

Is the credential checked on the lock or in the cloud?

On the lock, in every reputable design. PIN codes and paired phone credentials are stored in the lock module itself so that it keeps working when the internet is down. The cloud connection exists to give you remote status, remote unlock, notifications and code management — not to authorize a person standing at the door. That is why a smart lock still opens with its keypad during an outage, and it is the main reason a lock that cannot verify locally is worth avoiding.

What is the actual mechanism that turns the bolt?

A small brushed DC motor driving a reduction gear train, usually with a clutch so the interior thumbturn can still be operated by hand. The motor draws power only during the one to two second throw, which is why battery life is measured in months rather than days. If the bolt binds against the strike plate, the motor stalls under load, current draw jumps and the batteries drain far faster — misalignment is the most common cause of poor real-world battery life.

Do smart locks need a hub?

Wi-Fi and Bluetooth models do not. Z-Wave, Zigbee and Thread models do, because those radios have no direct route to the internet on their own — they talk to a hub or border router that bridges them. The trade is power: hub-based locks report roughly twice the battery life of locks carrying their own Wi-Fi radio, because a low-power mesh radio wakes briefly rather than holding an access-point connection open.

Are smart locks weaker than a normal deadbolt?

The bolt and strike are the same hardware, and BHMA grades residential deadbolts 1 through 3 on security, durability and finish regardless of whether electronics are attached. In practice the weak point on most residential doors is not the lock at all — it is a strike plate held by three-quarter-inch screws into soft jamb trim. Fitting three-inch screws that reach the stud frame is the cheapest meaningful upgrade you can make to any door, smart or not.

How Do Smart Locks Work? (Motor, Radio, Battery Explained)

Written & researched by Derek Holt Home & Appliances Editor

Updated September 2026

Overhead view of a person mounting a small camera beside a front door, in soft early-morning light

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A smart lock is a small electric motor attached to an ordinary deadbolt, plus a radio and a credential check. When you enter a code, tap the app or approach with a paired phone, the lock verifies that credential locally on its own chip, then drives a geared DC motor for one to two seconds to throw or retract the bolt. Everything runs on four AA batteries or similar. The radio — Bluetooth, Wi-Fi, Z-Wave, Zigbee or Thread — exists to report status and let you unlock remotely, not to decide whether the door opens.

What happens between the tap and the bolt moving?

Four steps, and only one of them involves the internet. The lock is designed so the credential check never leaves the device, which is what keeps it working during an outage.

Credential presented. A PIN on the keypad, a paired phone over Bluetooth, a fingerprint on the reader, or a command relayed from the app.
Verified locally. The lock compares it against codes stored in its own memory. No round trip to a server, no dependence on your router being awake.
Motor drives the bolt. A brushed DC motor turns a reduction gear train, throwing or retracting the deadbolt through a clutch that leaves the interior thumbturn manually operable.
State reported. Only now does the radio wake and push the new locked or unlocked state to the app or hub.

Wide environmental view of a person mounting a small camera beside a front door, in warm late-afternoon light

Which radio does what?

The radio determines remote access, battery life and whether you need a hub. It is the specification that matters most and the one buyers skim past.

Radio	Range	Hub needed	Remote unlock	Battery impact
Bluetooth only	About 30 ft	No	No — must be nearby	Lowest
Wi-Fi built in	Router coverage	No	Yes	Highest
Bluetooth plus plug-in bridge	Router coverage	Small bridge	Yes	Low
Z-Wave	Mesh, whole house	Yes	Yes, via hub	Very low
Zigbee	Mesh, whole house	Yes	Yes, via hub	Very low
Matter over Thread	Mesh, whole house	Border router	Yes	Very low

If you want the lock to work with Apple Home, Google Home and Alexa without picking a side, Matter over Thread is the specification to look for. Whether the lock keeps its core functions when the network drops is covered in do smart locks work without Wi-Fi.

Over-the-shoulder view of a person mounting a small camera beside a front door, in soft early-morning light

How do the different ways of unlocking compare?

Most locks support several at once, and the useful question is which one you rely on when the others fail. Codes are the workhorse: they need no phone, no network and no battery in your pocket, and they can be issued per person with a schedule attached.

Keypad code. Works offline, works for guests, works for a contractor between 9 and 5 on a Tuesday. The most reliable credential in the box.
Phone over Bluetooth. Convenient, but it depends on your phone having charge and the app having permissions.
Auto-unlock by geofence. The lock opens as you arrive. It is also the feature most often blamed for a door left unlocked, because a phone that crosses the geofence while you walk the dog can trigger it.
Fingerprint. Fast and popular, though owners consistently report worse recognition in cold and wet conditions.
Physical key. Present on most full-replacement deadbolts, absent on some slim designs. Check before you buy, not from the porch.

Low-angle view of a person mounting a small camera beside a front door, in soft early-morning light

Where does the power come from, and what happens when it runs out?

Four AA cells is the standard, mounted on the interior side. Because the motor only draws current during the throw, a Wi-Fi lock typically runs 3 to 6 months and a hub-based lock 10 to 18 — the radio, not the motor, is the drain. The detail is in how long smart lock batteries last.

For a dead battery, most locks provide an override: a key cylinder, external 9V contacts you touch a battery to, or a USB-C jump port. Identify yours now. On the security side, the electronics add an attack surface but not usually the easiest one, which we go through in can smart locks be hacked.

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More from this hub: Smart Home & Security · Best smart lock · Smart lock vs keypad lock · How to install a smart lock · How we rank

How Do Smart Locks Work?

Affiliate Disclosure

What happens between the tap and the bolt moving?

Which radio does what?

How do the different ways of unlocking compare?

Where does the power come from, and what happens when it runs out?

Frequently Asked