Quick Summary

The double cylinder deadbolt is the most argued about piece of hardware in a commercial building. It solves one real problem and creates a different one, and which of those matters more depends entirely on the door it is going on.

This guide covers how it differs mechanically, where it is genuinely appropriate, where it is restricted, and what you need to know before ordering parts. For the components of the lock itself, see our deadbolt parts guide.

What Is a Double Cylinder Deadbolt?

A deadbolt is a bolt with no spring in it. It does not retract when the door closes against the frame, and it cannot be pushed back by pressure on the end. The only way it moves is because something turns it. That is what makes it a deadbolt rather than a latch.

What varies is what does the turning. On a single cylinder deadbolt there is a keyed cylinder on the outside and a thumbturn on the inside. On a double cylinder deadbolt there is a keyed cylinder on both sides, so the bolt cannot be operated from either face without a key.

Everything else about the lock is the same. The bolt, the strike, the backset and the door prep do not change. What changes is the inside trim and therefore the behaviour of the door from the inside.

Why Would Anybody Fit a Double Cylinder Deadbolt?

One reason dominates: adjacent glass.

If there is a glazed panel in the door or a sidelight next to it, a thumbturn on the inside is reachable. Break the glass, put an arm through, turn the thumbturn, open the door. The lock has been defeated without any attack on the lock at all.

A double cylinder deadbolt removes that route, because reaching the inside face achieves nothing without a key. That is a genuine security improvement on storefront doors, rear doors with glazed panels, and any opening where the glazing was designed before anybody thought about the lock.

Secondary reasons come up too. Doors that lead to a secured area from inside the building, where you want the door controlled in both directions. Store rooms inside a public space. Doors where the occupant should not be able to unlock the way out casually.

Where Are Double Cylinder Deadbolts Restricted?

The objection is simple and it is about getting out, not getting in.

If the only way to unlock a door from the inside is with a key, then anyone inside without the key is held in. In an ordinary day that is an inconvenience. In a fire, with smoke and no light, somebody hunting for a key at a door they need to be through is a serious problem.

That is why free egress is a principle that runs through commercial door hardware. A person should be able to leave through an exit with one motion, without a key, without special knowledge and without tools. A double cylinder deadbolt is in direct conflict with that on any door used for egress.

The practical rules vary by jurisdiction and by occupancy, and your authority having jurisdiction is the one that settles it for a given building. What is consistent is the direction of travel: the more a door is relied on as a way out, the less acceptable a key operated inside becomes.

The Compromise Nobody Should Use

A habit exists of fitting a double cylinder deadbolt and leaving a key permanently in the inside cylinder during occupied hours. It defeats the purpose in both directions. During the day the lock is a single cylinder with a key sticking out of it, and the glass attack it was fitted to prevent now works again. At night, if the key is removed and somebody is still inside, you have the egress problem in full.

If egress is required, the answer is different hardware for that opening, not a procedure that depends on somebody remembering.

What Should You Use Instead on an Exit Door?

Classroom function is worth understanding properly, because it answers a different question from the deadbolt. Our classroom deadbolt guide covers the function and the cylinder options, and our exit device parts section covers the panic hardware route.

Does the Grade of the Deadbolt Change the Single Versus Double Decision?

No, but it changes how much the decision is worth.

Deadbolts are graded, and the grade describes how much abuse the lock will take before it fails. Within the Schlage B range, the B600 series is the Grade 1 family and the B500 series sits below it. Both are available in single and double cylinder versions, so grade and cylinder count are two separate choices made at the same time.

The point worth making on a glazed door is that upgrading the grade does nothing about the glass. A Grade 1 deadbolt with a thumbturn inside is defeated through a broken pane exactly as fast as a Grade 2 one.

Grade protects against force applied to the lock. Cylinder count protects against somebody reaching the inside. They answer different attacks, so the right choice depends on which attack the door is actually exposed to.

The Bolt and the Strike Have to Match the Ambition

A heavy deadbolt in a light frame moves the weak point rather than removing it. If the bolt is strong and well thrown but the strike is screwed into a thin jamb with short screws, the frame fails first. On an exterior door where the deadbolt is doing real work, the strike and its fixings deserve the same attention as the lock.

What Goes Wrong With a Deadbolt?

Deadbolts have very few moving parts, so the failure list is short and most of it is alignment rather than the lock.

The pattern worth remembering is that a bolt which throws freely with the door open and binds with it closed is an alignment problem, not a lock problem. Replacing the deadbolt will not fix it. Our commercial door hardware troubleshooting guide covers the strike and frame side of the same complaint.

How Do You Tell Which One Is Fitted?

Look at the inside face. A thumbturn is a single cylinder. A keyway is a double cylinder. That is the whole test and it takes a second.

For ordering, you need more than that. In the Schlage B series, the single cylinder and double cylinder versions carry different model numbers, and the replacement cylinders are listed against those models. A cylinder listed for a B562 is not the same order line as one listed for a B662, even though both are deadbolt cylinders, because they belong to different grades within the range.

Each cylinder is also listed against a door thickness range. The same model will have one cylinder for doors from roughly one and three eighths to one and three quarters inches, and a longer one for thicker doors. Ordering without measuring is the fastest way to get a cylinder that will not reach or will not tighten.

Can You Convert a Single Cylinder Deadbolt to a Double?

Often yes, because the change is at the inside trim rather than in the door prep. The bolt, the case and the hole through the door are usually common to both.

What you are replacing is the thumbturn with a keyed cylinder, which means a cylinder of the correct length for the door and, if the building is keyed, one that matches the existing key system. Conversion and adapter kits exist for exactly this.

Before doing it, answer the egress question for that specific door. A conversion that is mechanically straightforward can still be the wrong decision, and it is far easier to decide that before the thumbturn comes off than after an inspection.

Keying a Double Cylinder Deadbolt Into the Building

Two cylinders means two cylinders to key, and on a building with an existing key system that is not a detail to leave to the installer on the day.

Both sides should normally be keyed alike to each other, so one key works from either face. Beyond that, the deadbolt has to sit correctly in the building hierarchy so the right master keys operate it. Our master key system design guide covers the levels of keying, and the Schlage key systems guide covers the keyways and cylinder formats.

What to Confirm Before Ordering

1. Single or double, confirmed by looking at the inside face.
2. The model number from the lock, because grades within a range take different cylinders.
3. Door thickness, measured rather than assumed.
4. The keyway and key system, so the new cylinder works with the existing keys.
5. The finish, matched to the rest of the hardware on the opening.
6. Whether the door is an exit, which may rule the double cylinder out entirely.

Browse deadbolt parts and diagrams for the exploded views, or the full products and parts index if you have a part number. Our Schlage B series deadbolt parts guide covers the range in detail, and the labelled deadbolt diagram names every component.

About the Author

Security Parts has supplied repair parts for commercial door hardware since 2001, covering Von Duprin, LCN, Schlage, Falcon, Detex and Adams Rite at the component level. Our diagram based lookup exists so a technician can confirm a part before ordering it. This guide was written by the Security Parts team from supplier documentation and the questions our customers bring us.

For related reading, see our comparison of a mortise cylinder and a rim cylinder and the thumbturn cylinder guide.

Quick Summary

Keyed alike is one of those phrases that gets used loosely, usually to mean "I want one key for everything". That is sometimes exactly right and sometimes the start of a problem that takes years to unpick. The difference is whether the group of doors will stay small and stable.

This guide covers what keyed alike actually is, how it differs from master keying, when it is the better answer and when it is not. For the hierarchical alternative, see our master key system design guide.

What Does Keyed Alike Mean?

Keyed alike means a set of locks has been pinned to accept the same key. Turn up with that key and every lock in the set opens. Turn up with any other key and none of them do.

Mechanically there is nothing clever about it. A pin tumbler cylinder is pinned so that one particular cut of key lifts its pins to the shear line. Pin a second cylinder the same way and it accepts the same key.

The locks need not be the same type, or even the same product. A deadbolt, a cylindrical lever lock and a padlock can all be keyed alike to each other provided they take compatible cylinders.

That last point is what people miss. Keying happens at the cylinder, not at the lock. The lock body determines the function, the cylinder determines the key.

How Is Keyed Alike Different From Master Keying?

They sound similar and they solve different problems.

Keyed alike is flat. There is one key and there are no levels. Everybody who holds it can open everything in the group, and nobody can be given access to part of it.

Master keying is hierarchical. Each lock keeps its own change key, and a higher level key is added that operates a defined set of locks. Each cylinder is pinned so that more than one key cut will reach the shear line.

A department head's key opens their floor, a facilities key opens more, and the grand master opens the building.

They are not mutually exclusive. A master keyed building will often have small keyed alike groups inside it, so that a row of identical store cupboards share one change key while still sitting under the building's masters.

When Is Keyed Alike the Right Choice?

It works well when three things are true: the group is small, everybody who needs one door needs all of them, and that is unlikely to change.

• A suite of rooms used by one team. Office, store, and the door between them.
• Multiple entrances serving the same people. Front, rear and side doors of one unit.
• Equipment and enclosures. Cabinets, gates and padlocks that the same maintenance person opens on the same round.
• Doors with two locks. A lever lock and a deadbolt on the same leaf should almost always be keyed alike, so one key does the door.

That last one is worth calling out because it is the most common sensible use. A door with a deadbolt above the lockset is two locks, and if they take different keys then every entry and exit is a two key operation that nobody thanks you for.

When Does Keyed Alike Become a Problem?

The failure mode is always the same: the group grew, or the people changed.

Keyed alike has no way to withdraw access from part of the group. If one person should no longer have the store room, you cannot take the store room off their key. You can only take the key, which removes everything, or rekey the store room, which separates it from the group permanently.

Lost keys are the second problem. One key opens everything in the set, so losing one exposes every door at once. The remedy is rekeying every cylinder in the group, and the larger the group has quietly grown, the more expensive that morning becomes.

The third is drift. Keyed alike groups are rarely designed. They accumulate. Somebody adds one more door "while we are here", and five years later there are forty cylinders on one key and nobody is sure which doors are on it. At that point the building needs a key system rather than a habit. Our Schlage key systems guide covers what a designed system looks like.

What Happens When You Need to Add a Door Later?

This is where keyed alike groups quietly go wrong, so it is worth planning for on day one.

Adding a door to an existing keyed alike group is easy if you know the key code. A cylinder is pinned to that code, fitted, and the existing key works. It takes minutes and costs very little.

It is a different job if nobody wrote the code down. Then you are either taking an existing cylinder apart to read the pinning, or cutting a new key from an existing one and working backwards. Both are achievable and both cost more than the five seconds it would have taken to record the code when the group was created.

What to Record

None of that needs software. A sheet of paper in the facilities file is enough, and it is the difference between a twenty minute job and a day.

How Do You Rekey a Keyed Alike Group?

The honest answer is that you rekey all of it or none of it, and that is the whole argument for keeping these groups small.

Because every cylinder accepts the same key, changing that key means changing every cylinder. Leaving one behind means the old key still opens one door, which is usually the door you were worried about.

Three routes, in order of how much they cost you.

1. Swap interchangeable cores. If the group is built on removable cores, a control key pulls each core and a pre pinned replacement goes in. Fastest by a wide margin.
2. Repin conventional cylinders. Each cylinder comes apart and is repinned to a new code. Reliable, but it is a visit to every door.
3. Replace cylinders entirely. Sometimes the quickest option when cylinders are worn anyway, or when the group is being redesigned rather than just rekeyed.

Whichever route, take the opportunity to write down the new code and the door list. The reason the group was painful to rekey is almost always that nobody did that last time.

Which Cylinders Can Be Keyed Alike?

Any set of cylinders that share a keyway and a compatible pinning can be keyed alike to each other. In practice that means three decisions.

Cylinder format being different is not an obstacle. A rim cylinder on an exit device and a mortise cylinder on a lock body are built completely differently, and both can be pinned to the same key. Our comparison of a mortise cylinder and a rim cylinder explains how the two differ physically.

Why Interchangeable Cores Change the Maths

On a conventional cylinder, rekeying means taking the cylinder apart and repinning it, which is a locksmith job done at the door or on a bench.

An interchangeable core system changes that. The core is removed as a unit with a control key and a new core goes in. Rekeying a door becomes a thirty second swap rather than a service visit, and the old core can be repinned elsewhere at leisure.

That matters most for exactly the situation where keyed alike goes wrong. If a key is lost on a twelve door keyed alike group, conventional cylinders mean twelve repinning jobs. Interchangeable cores mean twelve core swaps, which one person can do in an afternoon. Our master key system design guide covers the core formats and how they differ.

What to Confirm Before Ordering Keyed Alike Cylinders

1. Which doors are actually in the group, written down rather than assumed.
2. The keyway, so one blank fits everything.
3. Pin count, consistent across the group.
4. Cylinder format for each opening, rim, mortise, key in knob or key in lever.
5. Whether the building already has a key system this group has to sit inside.
6. How many keys are needed, and who will hold a record of them.

Browse Schlage parts for cylinders and cores, or the full products and parts index if you already have part numbers.

About the Author

Security Parts has supplied repair parts for commercial door hardware since 2001, covering Von Duprin, LCN, Schlage, Falcon, Detex and Adams Rite at the component level. Our diagram based lookup exists so a technician can confirm a part before ordering it. This guide was written by the Security Parts team from supplier documentation and the questions our customers bring us.

For related reading, see the thumbturn cylinder guide and our deadbolt parts and diagrams.