What Is a Deadbolt Lock? | Solid Security Explained

For the full breakdown, see our best Deadbolt Locks guide.

When you lock your front door, a deadbolt is what stands between your home and someone trying to force their way in. Unlike a standard spring latch that retracts automatically when you pull the handle, a deadbolt’s bolt is “dead”—it has no spring action and won’t budge until you turn the key or thumbturn. That single design difference is why deadbolts are the go-to choice for exterior doors across American homes and businesses.

The trade-off is that a deadbolt is only as strong as its installation. Misaligned strike plates, shallow mortises, or improper drilling can leave the bolt short of the jamb and turn a solid lock into a decorative handle. Before buying, look through our roundup of the best deadbolt locks to see what holds up in real use.

How Does a Deadbolt Work?

A deadbolt works by sliding a solid metal bolt horizontally out of the lock body and into a recessed hole in the door frame, called the strike plate. Because the bolt has no spring, it stays extended until you deliberately retract it with the key, thumbturn, or lever.

The bolt’s length is what sets deadbolts apart. It extends far deeper into the door jamb than a spring latch, which makes it significantly more resistant to forced entry. A spring bolt, by contrast, can often be pushed back with a credit card or a sharp kick. A deadbolt holds firm.

That doesn’t mean it’s tamper-proof. A deadbolt resists common break-in methods like shimming and kicking, but a poorly installed lock—or one with a shallow bolt throw—can still be defeated. The hardware is only part of the equation.

Common Types of Deadbolt Locks

Deadbolts come in two main forms, each with its own trade-off between security and convenience.

Single-cylinder deadbolts use a key on the outside and a thumbturn on the inside. These are the most common residential option, letting you unlock from the inside quickly without hunting for a key—an important point for fire safety.

Double-cylinder deadbolts require a key on both sides. There’s no thumbturn at all, which means a burglar who breaks a window can’t simply reach in and unlock the door. That added security comes with a real cost: in an emergency, you need a key to get out. Local fire codes sometimes restrict their use on residential egress doors, so check your municipality before installing one.

There are also surface-mount deadbolts, which attach to the door’s face without drilling through the edge, and mortise-style deadbolts, which sit inside a pocket cut into the door itself. Surface-mount versions are common on metal doors or rentals where drilling isn’t allowed; mortise locks are more integrated and often found in older or higher-end homes.

What Goes Into Installing a Deadbolt?

Installing a deadbolt is a weekend project for a confident DIYer, but precision matters. The bolt hole, cylinder hole, and strike plate must all line up perfectly or the lock won’t throw its bolt cleanly.

• Drill the door-edge bolt hole and the cylinder hole through the face, using the bit sizes specified in the manufacturer’s instructions—these differ by model.
• Trace and mortise the latch plate so it sits flush with the door edge. A proud plate prevents the door from closing properly.
• Install the cylinder from the outside face, align the thumbturn on the interior side, and secure it.
• Mark and mortise the doorjamb for the strike plate so the bolt seats fully into the hole.
• Test the lock. The bolt should slide smoothly with no resistance, and the door should close without sticking.

Compatibility depends on your door’s thickness, material, and jamb depth, as well as the lock’s required hole diameter. A standard 2-1/8-inch bore hole fits most residential deadbolts, but always verify against the specific product’s specs before drilling. If you’d rather skip the measuring tape, our tested picks for best deadbolt locks highlight models with forgiving installation templates.