What is the Difference Between Single and Double Cylinder Door Locks?

The invention of the cylindrical lock changed the face of residential and commercial security forever.  For one hundred years the cylindrical lock has become the standard on doors all over the world.

Of course, as times change, so does the need for added security with flexible options that meet the needs of each individual property owner.  The development of two different types of cylindrical locks (single cylinder and double cylinder) reflects one of those needs.

Single cylinder locks are more common than double, though that trend is starting to change.  Single cylinder locks have only one lock cylinder, as the name implies.  Doors outfitted with single cylinders are unlocked with a key from the outside, but do not require a key for unlocking from the interior of the property.  Instead, the door is unlocked with a thumbturn-style lever.

Double cylinder locks contain two cylinders.  A key is required for locking and unlocking from both the exterior and the interior of the property.  There is no thumb-turn mechanism on a double cylinder lock.

As already mentioned, single cylinder locks are more common than double cylinder.  The two main reasons for this are efficiency and economy.  Single cylinder locks are usually less costly to purchase and install than double cylinders.  They are also more convenient, since there’s no need to hunt down a key to lock the door from the inside.  A simple thumb turn locks the door.

This may beg the question: why bother installing a double cylinder lock?  The main reason for doing so is enhanced security.  This is particularly true for doors that have locks which are located close to adjacent windows (i.e. an arm’s reach.)  A common problem with residential break-and-enters is proximity of windows to exterior doors.  Would be thieves need only smash the glass nearest the door, reach through, and unlock the thumbturn from the door’s interior side.  This makes for a quick and easy illegal entry.

Installing double cylinder locks on exterior doors eliminates this problem.  Since there is no thumbturn, thieves cannot reach inside to unlock doors manually through broken windows. 

Home and business owners typically cite “inconvenience” as the number one reason for avoiding the use of double cylinder locks.  However they may reduce the chances of break-and-enters by 50 percent or more.  Residential and commercial property owners who have any glass within an arm’s reach of door locks should consider installing double cylinder locks and/or deadbolts for an extra measure of protection.  When you consider the possible cost of NOT doing so, it’s usually worth the investment and the slight inconvenience.