What a deadbolt does that a doorknob lock does not
The lock built into a standard doorknob or lever holds the door closed with a spring latch, a beveled tongue that slides into the frame. That latch is designed for convenience, not security. It can be pushed back with a thin tool or forced with a pry, and the spring does not resist much. A deadbolt is different. It uses a solid bolt that extends into the door frame and stays there until the lock is turned back. There is no spring holding it in place, so it cannot be pressed back by pushing on the door edge.
Because the bolt is a solid piece of metal that moves only when the cylinder or thumb turn moves it, a deadbolt adds a meaningful layer of resistance. It is not unbreakable, and no residential lock is, but it requires real force or real skill to defeat, and that is the point of having one. Most people pair a deadbolt with the existing knob or lever so the door has a latch for everyday use and a bolt for security.
When you choose a deadbolt, you are choosing several things at once: the strength and build of the lock, how it is operated from each side, how long the bolt is, how well it fits your door, and how it will look and age. Each of those choices has trade-offs. The sections below take them one at a time, so you can match the lock to the door and the household, and avoid paying for features you will not use.
Understanding grades without the jargon
Residential locks are commonly sorted into three grades under a public standard used in the United States. Grade 1 is the strongest, built for heavy use and greater resistance, and it is common on commercial doors. Grade 2 sits in the middle and is a popular choice for homes that want better-than-basic hardware. Grade 3 is the lightest and is meant for ordinary residential use at the entry level.
The grade reflects how a lock performs in standardized tests for things like durability over many cycles, resistance to forced impact, and the strength of the bolt. It does not tell you everything about a lock, and two locks with the same grade can feel quite different in the hand. But it is a useful starting point, and a lock that states its grade is generally giving you something to compare. Our guide to lock grades explained goes deeper.
For a front door, a rear door that leads to a yard, or a door that opens to a street or walkway, a higher grade is worth considering. For an interior door that only needs a simple lock, lower grades can be fine. Consider the exposure of the door, who has access to it, and what is behind it. A garage entry door, for example, may be tucked away from view and deserve more strength, not less.
Keep in mind that the lock is only one part of the system. A strong deadbolt in a weak frame is limited by the frame. See the door frame security guide for why.
Single cylinder, double cylinder and the thumb turn question
A single cylinder deadbolt has a key slot 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 key slot on both sides, so a key is needed to operate it from inside as well.
The appeal of a double cylinder is that if a door has glass near the lock, a person who breaks the glass cannot simply reach in and turn a knob. The trade-off is serious: in a fire or other emergency, everyone inside needs a key to get out, and keys are easy to misplace in a panic. Many fire safety rules and safety guidelines discourage or restrict double cylinder locks on residential exits for exactly this reason, and rules vary by jurisdiction and building type. Check with your local building department or association before choosing one.
For most homes, a single cylinder deadbolt is the safer and more practical choice. If the worry is glass near the lock, there are other ways to handle it, such as a door with no glass within reach of the thumb turn, a security film on the glass, or a lock position that places the thumb turn out of reach. A technician can look at your door and suggest an arrangement that keeps the exit path simple.
If someone in the home has limited hand strength, arthritis or small hands, pay attention to the shape of the thumb turn. A larger, easy-grip lever can be more comfortable than a small knob, and comfort matters because a lock that is hard to turn gets left unlocked.
Bolt length, bolt material and what gets into the frame
The bolt is the part that does the work, and two measurements matter. The first is the throw, the distance the bolt extends beyond the door edge when locked. A longer throw gives the bolt more engagement with the frame and makes it harder to spread the door and frame apart. Many quality deadbolts have a throw of about an inch, and this is generally considered a good minimum for entry doors.
The second is the bolt material and construction. Solid steel bolts are common in better hardware. Some include hardened inserts inside the bolt, meant to resist cutting. Budget hardware may use lighter metals or hollow bolts that can be bent or cut more easily. The packaging will often tell you what the bolt is made from. If it does not, that is a sign to look elsewhere.
What the bolt goes into matters just as much. The strike plate is the metal plate around the hole in the frame, and its screws should be long enough to reach into the solid framing behind the door jamb, not just the thin trim. Short screws in a thin jamb are one of the most common weak points in homes. Upgrading to a heavy strike plate with long screws is a small change that adds a lot of strength to the whole system, and it applies to any deadbolt you choose.
Our strike plate reinforcement page explains how this is done.
Keyways, key control and picking resistance
The cylinder is the part that accepts the key, and it varies in quality. Standard cylinders use a pattern of small pins that line up when the correct key is inserted. Better cylinders use tighter tolerances, security pins that resist manipulation, and hardened parts that resist drilling and wrenching. They may also use keyways that are harder to copy or that are protected by restricted key blanks.
A restricted keyway system means that copies of the key can only be made through an authorized source, which helps with key control. This matters for landlords, property managers and anyone who wants to know where all the keys are. For a typical family home, a standard cylinder with decent build quality is often enough, but if you share keys with several contractors, rental guests or relatives, a restricted keyway can be worth considering. See high-security cylinders and the comparison in our guide on high-security versus standard locks.
We do not give instructions on defeating locks, and a guide like this is not the place for them. What matters for a buyer is simpler: choose a lock from a maker that stands behind its design, avoid unmarked or no-name hardware, and avoid cylinders that feel loose, rattle, or have a rough key action in the store. A smooth, tight action is a decent sign of tight tolerances.
Finally, think about how many keys come in the box and how many you really need. If you will be giving out keys, plan for a way to track and recover them.
Fit: door thickness, backset and bore holes
A deadbolt is only as good as its fit in the door. Before you buy anything, measure or confirm three things. The door thickness should be within the range the lock supports, and most standard entry doors are within the common range. The backset is the distance from the edge of the door to the center of the large hole that holds the lock, and it is usually one of two standard sizes. The bore hole size and the cross bore, the hole through the door edge for the bolt, should match.
If you are replacing an existing deadbolt, the holes are already there and the new lock needs to fit them. Most replacement deadbolts are designed to fit standard holes, but older doors, custom doors and impact doors can differ. If the existing hole has been enlarged or damaged by a prior forced entry, a new lock may sit loose, and a technician may need to repair the door before installing the lock.
Fit also includes the strike side. The bolt has to align with the hole in the frame, and the frame has to be square. A door that has shifted may need hinge adjustments before any lock will work smoothly. Many homeowners buy a good lock, install it, and then find it binds because the door was never quite aligned. A professional installation takes this into account. Read about the process on the deadbolt installation page.
If your door is unusual, such as a narrow stile glass door, a metal security door or an impact-rated entry, mention it when you call, so the right hardware is selected.
Finish, corrosion and Florida weather
In South Florida, finish is not just about looks. The finish is the first defense against humidity, salt air, sun and rain, and it plays a role in how long the lock keeps working. Plated finishes vary a lot in quality. A thin plating can pit and flake in coastal air, and once the underlying metal is exposed it corrodes quickly.
Options that tend to hold up better include solid brass hardware, stainless steel, and finishes designed for outdoor or marine exposure. A door facing the water, a balcony door, or a door with direct weather exposure benefits the most from those. A door under a deep covered entry is less demanding, but interior mechanisms are still affected by humidity.
Match finishes across the entry set as well. A deadbolt and a handle set that clash in color or age differently can look mismatched. Many makers offer matching finishes across locks and handles, which keeps things tidy. If you have a historic or custom home, finish matching may matter even more, and some finishes need to be ordered.
Think about maintenance too. A lock that gets an occasional dry lubricant and a wipe-down will last longer than one left alone. Our guide on caring for locks in salt air offers practical steps. Choose a finish you are willing to keep up.
Keyed alike, smart options and future flexibility
If you have several exterior doors, you may want them to use one key. Keyed-alike deadbolts are made so that a single key operates multiple locks. That is convenient, but it also means one lost key affects every door that uses it. Weigh the convenience against the risk, and consider whether rekeying later would be easy. Our guide to keyed alike locks covers the trade-offs.
Electronic and smart deadbolts add keypads, app control or automatic locking. They can be useful for guests, rentals, and families who lose keys, but they need power, either batteries or wired, and in humid climates the electronics deserve attention to build quality. If you like the idea, compare options and consider whether you want a backup key. See smart lock, keypad or key for the comparison.
Think about what you may want later. If you might sell the home, a lock that is easy to rekey is helpful, because rekeying after a sale or a move is routine. If you may rent the property, a lock that allows changing keys without replacing hardware may save work later. If you may add a smart lock down the road, ask whether the deadbolt you choose can be upgraded or whether the door prep is compatible.
None of this needs to be settled all at once. A plain, well-built single cylinder deadbolt is a good base, and many people never need more.
A simple decision path and common mistakes
If you want a quick way through the decision, start from the door. Identify the door material and thickness, and confirm whether the existing holes are standard. Decide on single cylinder unless there is a specific reason and your local rules allow otherwise. Choose a grade appropriate to how exposed the door is. Choose a finish that suits your location. Then look at the strike plate and frame, because they decide how much of the lock's strength you actually get.
Common mistakes are easy to spot once you know them. Buying the lowest-grade lock that fits is the first, because a flimsy bolt and cylinder do not resist much. Ignoring the strike plate is the second. Using short screws is the third. Putting a double cylinder on a door with an exit requirement is the fourth. Choosing a finish that is not suited to the coast is the fifth. Installing without checking the door alignment is the sixth.
A good deadbolt installed correctly is not a complicated project, but there are enough small details that many people prefer to have a technician do it. A technician will also check that the old hardware is removed cleanly and that nothing else about the door is hiding a problem. Whether you do it yourself or have it done, the choices above apply.
If you would like help deciding, call and describe your door. We can talk through the options, explain what is available, and give you a quote by phone. Complicated jobs may need an on-site visit, and the service call charge is explained before anyone is dispatched.
- Identify the door material, thickness and existing hole sizes.
- Choose single cylinder unless local rules and a clear reason say otherwise.
- Match the grade to how exposed the door is.
- Pick a finish suited to coastal weather.
- Check the strike plate, screws and frame alignment.
- Decide how many keys you need and who will hold them.
Questions people ask
Is a double cylinder deadbolt a good idea for a door with glass?
It can stop someone from breaking the glass and reaching in to turn a thumb turn, but it also means a key is needed to leave. In a fire or emergency that can be dangerous, and some local rules restrict them. Many homes are better served by a single cylinder lock plus glass protection. Ask your building department or association before choosing one.
Does a higher grade deadbolt really make a difference?
A higher grade generally means better durability and stronger resistance to forced impact, based on standardized tests. It is most useful on exposed doors such as front, rear and garage entry doors. Still, the strike plate, screws and door frame matter just as much, so a high grade lock in a weak frame is limited by the frame.
How long should the bolt be?
A bolt that extends about one inch into the frame is commonly considered a good standard for entry doors. A longer throw gives more engagement and makes it harder to spread the door and frame. The bolt also needs to line up with a strong strike plate that is screwed into solid framing, not just the thin trim around the jamb.
Can a smart deadbolt replace a regular one on any door?
Often, but not always. Many smart deadbolts fit standard door preparation, but unusual thickness, narrow stiles, metal doors or impact doors may need adjustments. You also need to plan for batteries or power and for a backup way in. Call with the door details and we can tell you whether a smart lock will fit.
Should all my exterior doors use the same key?
It is convenient, because one key opens everything, but it also means one lost key affects every door. Some households prefer separate keys for different doors, and others rekey when a key goes missing. Rekeying is a routine job, so keyed alike is not a trap, but it is worth thinking through before you choose.
How do I get a price for installing a new deadbolt?
Quotes are given by phone. Tell us about the door, the existing lock and what you want, and we will explain the options and the cost. If the job looks complicated, such as a damaged door or unusual hardware, an on-site visit may be needed. A service call charge applies and is explained on the phone before dispatch.
Describe the situation by phone and we will tell you what the job involves. Quotes are given by phone. Jobs that cannot be quoted without seeing them need a technician on site, and the service call charge is explained on the phone before anyone is dispatched.
(954) 906-9567