Types of Residential Door Locks | What Actually Secures Your Home

Choosing the right door lock for your home means knowing what each type does well and where it falls short. The lock on your front door is your first line of defense, and the wrong choice can leave a house vulnerable in ways most homeowners never think about until it’s too late.

Whether you’re replacing an existing lock, building a new home, or upgrading for better security, this guide breaks down the five main types of residential door locks—what they are, where they work best, and the trade-offs you need to know before buying.

Single-Cylinder and Double-Cylinder Deadbolts

Deadbolts are the backbone of residential security. A deadbolt extends a solid metal bolt into the strike plate when you lock it, which makes it much harder to force open than a spring latch. This mechanical principle is what separates a deadbolt from a basic knob lock.

Single-cylinder deadbolts have a key cylinder on the outside and a thumbturn on the inside. You lock and unlock the exterior with a key, and simply twist the thumbturn from inside. This is the most common deadbolt type in American homes, and for good reason—it’s simple, reliable, and allows quick exit in an emergency.

Double-cylinder deadbolts require a key on both sides. There’s no thumbturn on the interior at all. These locks exist for one specific scenario: doors with glass panels or sidelights. If an intruder breaks the glass, they can’t simply reach in and turn a thumbturn to unlock the door. The key requirement stops them cold.

But that same feature creates a real safety risk. In a fire or other emergency, occupants need a key immediately to escape. If keys aren’t right there, a double-cylinder deadbolt can trap people inside. Building codes in many jurisdictions actually restrict where these locks can be installed for exactly this reason.

Knob, Mortise, and Interconnected Locks

Key-in-knob locks (also called tubular locks) are the most basic residential lock type you’ll find. The key cylinder sits right in the door knob or lever. These are common on interior doors and secondary exterior doors, but security experts generally don’t rely on them as the sole lock on a front door. The spring latch mechanism is easier to force than a deadbolt.

Mortise locks are a different animal entirely. Instead of fitting into a bored hole, a mortise lock is embedded directly into a cavity cut into the door edge. The lock body sits inside the door with the handle and key cylinder attached on either side. Mortise locksets are widely considered the strongest residential locks available—they’re common in commercial settings and in high-end or older residential construction.

One catch: mortise locks require a door that’s prepped with that edge cavity. You can’t simply swap a bored cylindrical lock for a mortise lock without significant door modification.

Interconnected locks combine a deadbolt and latch in a single unit. The defining feature is life-safety: lifting or turning the inside knob retracts both the latch and the deadbolt at once. That means in an emergency, one motion unlocks the door completely. No fumbling with a separate deadbolt thumbturn while a fire or other threat is bearing down on you.

Smart Locks and Retrofit Options

Smart locks replace the traditional key with digital access methods—smartphone apps, keypads, fingerprint readers, or voice commands. Allegion’s door hardware education resource breaks smart locking systems into two distinct categories.

Full smart locks replace the entire deadbolt hardware. The deadbolt itself is new, with the electronics built directly into the lock body. These give you the most features but require replacing your existing hardware completely.

Retrofit smart locks attach to your existing deadbolt. They mount over the thumbturn on the inside of the door and motorize it. You keep your current exterior key cylinder and deadbolt, and the retrofit unit handles the smart functionality. This is the lower-cost, lower-effort path for adding smart features to an existing lock.

Before buying, check compatibility—not just with your door, but with your phone’s operating system and any smart home hub you use. Smart locks run on batteries and depend on electronics, so a conventional backup key is still your safety net when those fail.

Choosing the Right Lock for Each Door

Different doors on your home have different security needs, and matching the lock type to the entry point matters more than buying the single “strongest” option for everything.

Front Door and Main Entry

The primary exterior door should have a single-cylinder deadbolt as the base. It’s the standard for good reason: exterior key access, interior thumbturn for fast exit, and solid bolt security. If your door has glass panels or sidelights within arm’s reach, consider a double-cylinder deadbolt despite the egress trade-off.

Upgrading from a basic knob lock to a deadbolt on the main entry is one of the highest-impact security improvements you can make. Home security experts consistently recommend it as a first step before any other lock upgrade.

Secondary Doors, Sliding Doors, and Windows

Back doors, garage entry doors, and basement doors often get neglected. These are common break-in points precisely because they’re less secured than the front door. A Wikipedia overview of lockset types notes that night latches and rim automatic deadlatches typically serve as supplemental security rather than a standalone high-security front-door solution.

Beyond lock types, one detail matters for installation: door handing. Facing the door from outside, if the hinges are on the left, it’s a left-handed door; on the right, right-handed. Getting this wrong means buying the wrong latch direction, and a surprising number of DIY installs fail on exactly this point.

For homeowners narrowing down a purchase, a Schlage B-Series datasheet illustrates how manufacturers position their lock lines by security tier. When comparing locks, look at the ANSI/BHMA grade: Grade 1 is the highest-duty rating, Grade 2 is mid-grade residential, and Grade 3 is the minimum residential grade.

If you’re ready to buy, our tested picks for the best home security door locks break down which models actually perform well in real-world use.

FAQs

Can a smart lock replace a traditional deadbolt?

Yes, but the answer depends on the type you choose. A full smart lock replaces the entire deadbolt assembly and functions as your primary lock. A retrofit smart lock attaches to your existing deadbolt and simply motorizes the thumbturn, keeping your current exterior key cylinder. Both require battery power and phone or hub compatibility, so always verify those details before purchasing.

Are double-cylinder deadbolts legal in all states?

Double-cylinder deadbolts are legal in most states, but building codes in many jurisdictions restrict their use on residential egress doors because of the fire safety risk. Exiting requires a key from the inside, which can trap occupants in an emergency. Check your local building code before installing one on any door that could be an exit path.

What’s the difference between Grade 1 and Grade 3 locks?

ANSI/BHMA grading measures a lock’s durability and security performance. Grade 1 is the highest duty rating, designed for heavy commercial use with the most rigorous cycle testing and force-resistance requirements. Grade 2 is mid-grade, suitable for residential doors that see regular use. Grade 3 is the minimum residential standard. For most homes, Grade 2 deadbolts offer an excellent balance of security and value.