Installing a Deadbolt That Actually Holds

What a deadbolt does that a doorknob does not

The knob or lever on most doors controls a spring latch, a small angled bolt that holds the door closed. The latch is designed for convenience. It is shaped so that the door can be pushed shut and will catch automatically, and that same shape makes it easy to push back, which is why a latch alone is not security. A deadbolt is different. It is a solid metal bolt that has no spring and no slope. Once it is thrown into the frame, it stays there until the key or thumb turn pulls it back.

That difference is the point. A deadbolt resists being pushed back, so it holds a door shut against casual attempts to open it. When paired with a solid door, a strong strike plate and a good frame, it is the main line of defense on an exterior door. Most insurance and security advice for homes recommends one on every exterior entry.

A deadbolt does not make a door invincible. A determined attack on a weak door or frame can succeed, whatever lock is on it. But most break-ins are quick and opportunistic, and a well installed deadbolt in a sound door makes the job harder and slower, which discourages many attempts.

This page covers the choices and the installation details that decide how well a deadbolt performs. Our page on lock change and installation gives the wider picture for a whole door, and our guide on how to choose a deadbolt helps you compare models.

Single cylinder or double cylinder

The first decision is how the deadbolt operates from inside. A single cylinder deadbolt has a keyhole on the outside and a thumb turn on the inside. You can lock or unlock it from inside by hand without a key. A double cylinder deadbolt has a keyhole on both sides, and a key is needed to operate it from either side.

Weighing the safety trade-off

The argument for a double cylinder is simple. If your door has a window in it, or a window right next to it, an intruder can break the glass, reach in and turn a thumb turn. With a key-only interior, that does not work. That is a real benefit for some doors.

The argument against is just as real. In a fire or a medical emergency, every second counts. Finding a key in smoke or panic is hard, and if the key is not in the lock, people can be trapped. Fire safety guidance generally warns against leaving a double cylinder deadbolt locked without the key in it, and some building and fire codes restrict or prohibit double cylinder locks on residential exit doors. Rules differ by place and by building type.

A practical compromise for a door with glass is to choose a single cylinder deadbolt and change the door. Another option is to fit a security film or laminated glass to the pane, or to choose a door without glass. A third is to use a thumb turn that cannot be reached from outside the broken pane, by positioning it carefully, though this depends on the layout.

If you consider a double cylinder, keep a key in a fixed, known spot near the door but out of reach of a broken window, and make sure every adult in the household knows where it is. Check your local code before you decide. We cannot give legal advice, but a technician who works in your area usually knows the local practice. Ask when you call.

Throw length: how far the bolt goes into the frame

The throw is the distance the bolt extends from the edge of the door when locked. A longer throw digs deeper into the frame and resists being pushed or pried out. Common deadbolts have a shorter throw. Many security oriented models have a longer one. A longer throw is generally better, as long as the frame can accept it.

Throw length alone is not the whole story. A long bolt in a weak frame is only as good as the wood it reaches. The bolt must go into a solid piece of framing, not just the thin trim around the door. If the strike plate is held by short screws into trim, a hard kick can split the trim and the door opens even though the bolt held. That is why the strike plate and the screws matter at least as much as the bolt.

Bolt material and shape also matter. Some deadbolts have a hardened steel insert that resists sawing, and some have a bolt that rotates freely so a saw blade cannot bite. Ask the technician about the options, and ask how the lock is rated.

You also want a clean fit. The bolt should extend and retract smoothly and be neither too tight nor loose in the hole. If the bolt must be forced into the strike because the door sags or the hole is misaligned, wear and failure will follow. A careful installation takes the time to line things up. A technician measures the door and frame and chooses a lock that suits.

Strike plate reinforcement

The strike plate is the metal plate in the door frame that the bolt goes into. It protects the wood around the hole, and it is where the force of a kick or a shove ends up. A standard strike plate is often a thin piece of metal held by two short screws that go only into the door trim. Under force, the trim can split and the plate tears loose.

Reinforcement fixes this. A technician can fit a heavier strike plate, with long screws that pass through the trim and into the wall stud behind, which is a much stronger piece of wood. Some reinforcement kits include a longer metal plate that spreads the force along the frame. Others wrap the frame edge in metal. In some cases, a metal reinforcing plate on the door edge around the lock is also used.

Reinforcement also applies to the hinge side. Hinges are held by screws too, and short screws into thin trim are a weak point. A technician may replace one or two hinge screws with long ones that reach the stud, which strengthens the door overall.

Reinforcement does not change how the lock looks or works. It changes how much force the door can take before it fails. For most homes, long strike screws are the single most useful improvement for the cost of a few minutes of work. A technician will explain what they recommend for your frame, and you can decide.

Checking the door and the frame first

A deadbolt installation begins with the door. The technician checks the thickness, the material and the condition. A solid wood door, a steel door and a fiberglass door each take a deadbolt differently. A hollow core door, common indoors, is not suited to an exterior deadbolt, since the thin skins and empty center give no support to the lock.

They check the frame. Is the wood sound, or is it cracked, rotted or split from a past kick? Is there a gap between the door and frame that the bolt must bridge? Is the door square, or does it rub or sag? A door that does not close properly will make a deadbolt work poorly. Fixing a sagging hinge, adjusting a strike or planing a door edge may be needed before the lock can work as intended.

They check the existing holes. If there is already a deadbolt, the holes may be the right size. If not, new holes are drilled to the standard dimensions, using a guide so they are straight and centered. A crooked hole causes the bolt to bind and the lock to fail early.

Where the door has glass nearby, the technician notes how close the glass is to the thumb turn and tells you the options. If the door or frame is badly damaged, they will tell you honestly that repair or replacement of the door is the better first step. Our page on lock repair after a break-in describes this situation.

What a careful installation includes

A good deadbolt installation follows a sequence. The technician marks the position of the lock at a convenient height, typically above the existing handle, with enough distance to leave the door strong between the two holes. They drill the large cross bore for the lock body and the smaller edge bore for the bolt, using the right size of cutter for the door material.

They cut a shallow recess in the door edge for the faceplate so it sits flush. They install the bolt and the lock body, connect the outside cylinder and the inside part, and tighten the through screws so that the lock is firm but not binding. They then fit the strike plate in the frame, cutting a recess, drilling the bolt hole deeper than the bolt will travel, and fixing the plate with long screws.

Finally they test. They turn the key and the thumb turn, watch the bolt move, close the door and lock it, and check that the bolt goes in cleanly with no need to lift the door. They test every key. They check that the door closes smoothly and that the existing handle and latch still work.

A technician will explain how the lock operates, tell you about any extra features and answer your questions. Quotes are given by phone, and where a job is complicated, an on-site visit may be needed to assess it. The service call charge for that visit is explained before anyone is dispatched.

Unusual cases: glass doors, sliders and garage entry doors

Not every door is a standard wood or steel slab. Glass panel doors need extra thought. A deadbolt on a door with a large pane next to the lock is vulnerable if the glass can be broken and the thumb turn reached. Options include a double cylinder where code allows, laminated or security glazed glass, a security film, or a different door. A technician can discuss what suits your layout.

Sliding glass doors do not take a standard deadbolt. They use a different set of locks, such as a secondary bar, a pin lock or a surface mounted lock. These are different products, and a technician can advise on what suits your slider.

A door between a garage and the house is another case. It is often a solid door with a deadbolt, but it may be fire rated, which limits the changes you can make. Our page on garage entry door lock problems covers common issues there. Check with the technician before drilling a fire rated door.

French doors, double doors and doors with a narrow stile have their own requirements. A narrow stile limits the lock size, and double doors may need a flush bolt on the inactive door. A technician will check and explain.

Keeping a deadbolt working well

A deadbolt needs little care, but a few habits keep it reliable. Use it. A deadbolt that is not thrown does not protect. Make it a habit to lock it whenever you leave and at night.

Operate the lock fully. Turn the key or thumb turn until the bolt is completely extended. A half-thrown bolt gives a false sense of security. Do not slam the door in a way that forces the bolt against the frame, because that wears the lock and the strike.

If the bolt begins to stick or the key becomes hard to turn, look at the door first. Seasonal changes in humidity can make a door swell and shift, so the bolt no longer lines up with the strike. If the door has moved, a technician can adjust the strike or the hinges. Do not force the key, because a worn or bent key can break in the lock.

A light puff of dry lock lubricant now and then is enough. Avoid heavy oil or grease, which collects dust. Check the screws on the strike plate and hinges once a year and tighten any that are loose. Replace worn keys, since they wear the pins inside the lock.

Our page on a deadbolt that will not turn explains the common causes and what to do if yours has begun to stick.

What to have ready when you call

The person on the phone can work out the job more quickly if you can describe the following.

• How many deadbolts you want installed or replaced, and on which doors.
• The material of each door: wood, steel, fiberglass, glass panel or aluminum.
• Whether the door already has a deadbolt hole or you need a new one.
• Whether there is glass in or next to the door.
• The condition of the door and frame, including any splits, rot or earlier damage.
• Your preference between single and double cylinder, or whether you want advice.
• Whether you want the new lock keyed to match other locks.
• Proof that you own the property or have the right to authorize the work.

Call to talk it through

If you are weighing up a deadbolt, a short call can answer most questions. Tell the person on the phone about your door and what concerns you. They will explain the options, tell you whether a visit is needed and give you a quote by phone. We do not publish prices or ranges online, and we do not promise arrival times.

When you are ready, call. Describe the door, the frame and what you would like to achieve, and we will help you choose a deadbolt and an installation that suits your home.

Questions people ask

Related pages

Written by Claude (AI) (AI) for 24/7 Locksmith USA.