Single Cylinder vs Double Cylinder Deadbolt Is a Question About Getting Out

For the door your household uses to get out, choose a single cylinder deadbolt: a key outside, a thumb turn inside. The single cylinder vs double cylinder deadbolt choice is usually framed as convenience against security, but the real trade is how fast someone inside can leave in the dark. The one condition that changes the answer is a door with glass near the lock that nobody uses as an exit, and even there, check your local code before you order a double cylinder.

What the second cylinder changes

A deadbolt is a bolt with no spring. It moves only when a key or a thumb turn throws it, which is why pushing on the end of it does nothing, unlike the angled spring latch below it. The cylinder is the keyed part. A single cylinder deadbolt has one, on the outside, and a thumb turn on the inside. A double cylinder deadbolt has a keyed cylinder on both sides and no thumb turn at all, so throwing or withdrawing the bolt from either side takes a key.

That is the whole mechanical difference, and it is a large one. The bolt, the strike and the door are the same. What changes is who can open the door from inside, and how.

Emtek offers both on its tubular entry sets, along with a dummy function for the fixed half of a pair of doors. One detail worth knowing before you order: Emtek's interconnect option, which lets the inside knob or lever pull back the deadbolt and the latch together, is available only with single cylinder sets. A double cylinder cannot be linked that way, because there is no thumb turn to link.

The glass argument, taken seriously

The case for a double cylinder is specific and real. If a door has a glass panel, a sidelight or a transom close enough to the lock, someone outside can break the glass, reach in and turn the thumb turn. A keyed cylinder inside removes the thumb turn to reach for.

Notice what that argument depends on: glass within an arm's reach of the lock, and the key not left in the inside cylinder. A common workaround is to leave the key in the inside cylinder or hang it right beside the door so nobody gets trapped, which puts the reach-through risk straight back. If the key stays in the lock, a double cylinder costs you the thumb turn and buys you very little.

The same logic applies to the interconnect option in reverse. On a door with glass near the lock, a single motion on the inside lever opens the door for anyone who can reach it, so think about the glass before adding that convenience.

My view is that the glass problem is usually better addressed at the glass and the door than at the key. Ask the door maker or a glazier what glazing options exist for your door, and have an installer look at the strike and the frame, since a bolt is only as useful as what it locks into. None of these is a guarantee, and neither is a double cylinder; they are ways of making a reach-through harder without making the exit harder.

The cost: a key between you and the door

The tradeoff of a double cylinder shows up at the worst possible time. In a fire, smoke or any emergency at night, everyone inside has to find a key, in the dark, possibly with a child in one arm, before they can open the door. Guests, sitters and older relatives may not know where the key lives. A thumb turn needs none of that: feel for it, turn it, go.

That is also the cost of my own recommendation. A single cylinder leaves the thumb turn where a hand through broken glass could find it. I would still choose that risk on the exit door over the risk of being unable to get out of it, and work on the glass separately.

What the codes say, and why you still have to ask locally

There is no single national rule to quote, and this is where many of the ranking pages go vague or wrong. What is widely documented is this: the International Residential Code, which many US jurisdictions adopt with their own amendments, requires the egress door of a dwelling to be readily openable from inside "without the use of a key or special knowledge or effort" (section R311.2). A keyed-inside deadbolt on that door is hard to square with that language, which is why many residential codes restrict double cylinder locks on exit doors.

But codes are adopted, amended and enforced locally, and door hardware code consultants say it plainly: residential requirements vary with the code in use where you live. Which door counts as the required exit, whether other doors are covered, and what applies to rentals are all questions for your local building department or a licensed locksmith or installer who works in your area. Ask before you buy, not after the inspector does.

Walk the way out at night before you decide

Here is the test I would run before ordering either lock. After dark, with the lights off, walk from the farthest bedroom to the door you would use to get out. Note how long it takes and what you touch. At the door, ask two questions.

• Could every person in this house open it from here, without help? Count children, guests and anyone with stiff hands. If the answer depends on finding a key, that door wants a single cylinder.
• How close is the nearest glass to the lock? Stand outside and measure from the nearest pane to the spot where the thumb turn sits inside. If no arm through any pane could reach it, the glass argument does not apply to this door at all.

Repeat the walk for each exterior door. If every door people actually use passes, a single cylinder throughout keeps one key and one habit for the whole house.

Where a double cylinder can make sense

The narrow case is a door that nobody relies on to get out, with glass near the lock, where your local code allows a keyed-inside lock. A rarely used side door with a glass panel, in a house with another clear exit, is the kind of door this describes. Even then, keep a key where every grown-up living there can locate it in the dark, out of reach of anyone outside the glass, and accept that it will be slower to open than every other door in the house.

If you rent, own a property with tenants or share the house with someone who could not manage a key quickly under stress, talk to the building department first. Those are the situations where the rules and the risks both tighten.

Buying the deadbolt itself

Once the function is settled, the hardware follows the door. A standalone deadbolt set fits the upper bore of a door drilled for tubular hardware and lets you choose the function without touching the latch. If you are replacing the whole front door set, the deadbolt comes built into a handleset or entry door set, and you choose single or double cylinder as an option on the order. Emtek lists both on its entry sets, so the decision above, not the catalog, is what narrows the list.

Measure the backset (how far the center of the bore sits in from the door's edge), confirm the door thickness, and match the deadbolt finish to the other pieces on the door. Then make sure everyone in the house knows how the door opens from inside, whichever lock you choose.