Tech Tips: Lock Functions

April 25, 2022
Security pros should know what they’re for and how they work.

In door hardware, the term “function” defines how the locking device operates.

Familiarity with lock functions is critical if you’re involved with door controls, life safety and electronic access control (EAC) systems, because mechanical and electromechanical locks are still and probably will continue to be, essential ingredients in physical security.

In security, we also use the term “function” to describe how devices that are combined to work together operate. If your work includes mechanical locks, accurately describing how the lock is supposed to function is a good starting point.

Because physical security is a dynamic technology, new functions are added frequently. There are more than 60 ANSI lock functions today among cylindrical and mortise locks and exit devices.

The Standards

In the case of cylindrical locks, mortise locks and exit devices, the relevant standards are:

  • ANSI/BHMA A156.2-2017 (for bored and preassembled locks and latches)
  • ANSI/BHMA A156.13-2017 (for mortise locks and latches)
  • ANSI/BHMA A156.3-2020 (for exit devices)
These documents define terms, list the lock functions and explain the testing steps to be performed on items submitted for certification.

If you’re involved with specifying locks, you might wish to purchase the standards that are relevant to your areas of locksmithing. You also might obtain information on lock functions from the lock manufacturers, and lock distributors are excellent sources of technical support.

After you’ve documented how the lock will be required to operate, you can find an ANSI function that most closely matches your requirements.

My own activities in security frequently involve integrating mechanical locks with electronic devices to arrive at more-complex solutions, and I used the expression “theory of operation” to define my process.

While the project was still in a conceptual phase, using the word “theory” sounded tentative and wishful, but after the design was complete and debugged, it wasn’t a theory any longer, but a fact. The theory of operation detailed how the system would operate when it was installed professionally, used properly and operated correctly.

For example, when it’s desired to unlock a door electrically, a mechanical lockset might be combined with an electric strike. Thus, you could come up with a “theory of operation” you could review to determine that the solution complies with building and life-safety codes while fulfilling the client’s expectations.

Cylindrical locks have a latch, two knobs, one or two lock cylinders (key in knobs) or a turn piece on the inner knob, so lock functions typically are simple and limited. But we also use mortise locks and exit devices, which have other features, such as deadbolts, and other means of controlling them, such as trim. We also might integrate the lock with keypads, timers and status indicators. The large number of available ANSI lock functions reflects the extensive number of combinations that are possible.

Note that although there are many ANSI functions and they’re published as three distinct categories, the majority of locks we use have fewer than 10 possible functions. In other words, many of the ANSI functions are for specific applications.

But lock manufacturers also apply their own numbering systems to organize their locks’ functions, so having a familiarity with the basic functions and the terminology will help security pros to deal with the challenges likely to be encountered when working with locking device specifications. That’s because, occasionally, a manufacturer’s function code won’t match up with an ANSI function code, and you’ll have to sort out the differences. (It always amazed me how many individuals involved in EAC and system integration have little interest in acquiring knowledge about locks and lock functions.)

When in doubt, consult the manufacturer’s catalog.

Lock Functions

As security management demands become increasingly complex, so, too, can be the solutions.

Many different lock functions are available, but the majority of locks specified include one of six primary mechanical functions. Nevertheless, having exposure to and an understanding of all functions will enable you to best advise and service your clients. Here are the six primary functions.

Passage Sets. In a passage set, there’s no key cylinder and no means to lock it. These are used where doors have to remain latched but don’t have to lock.

Privacy Sets. Privacy sets often are used for single-occupant restrooms or dressing rooms. They can be locked from the inside via a thumbturn or a push-button or turn, and they typically are unlocked from the outside by using a tool rather than a key. One variant of this function is the hospital privacy set, which has a thumbturn on the inside and outside to allow hospital staff to have quick access to a bathroom. Such functions also might incorporate an indicator to show the locked status of the door.

Storeroom Locks. For storeroom locks, the outside lever remains locked at all times. A key retracts the latchbolt and allows you to open the door. When the key is released, the door is relocked.

Office Locks. Office locks may be controlled by a key in the outside cylinder or by a thumbturn or push-button or turn on the inside. The outside lever may be left in a locked or unlocked position. The use of the thumbturn or button provides convenience to the user but also might allow an unauthorized person to control the lock, so this lock should be used where unauthorized use isn’t a concern.

Classroom Locks. Classroom locks are controlled by a key in the outside cylinder, which locks or unlocks the outside lever. The lock can be left locked or unlocked by using a key.

Classroom Security Locks. Classroom security locks are a relatively new function. They allow control of the outside lever via a key cylinder on the inside and outside of a door. Locks that have this function are great for where it isn’t desirable to leave a room to lock the door.

When it comes to electrified locksets, two functions that you probably are well-aware of are the most commonly used: electrically locked (fail-safe) or electrically unlocked (fail-secure). When electricity is applied to a mortise lock, for example, the outside lever is locked, but the inside lever always allows free egress (fail-secure). When electricity is removed from the lock, the outside lever is unlocked, which makes it fail-safe. The locking of the outside lever also can be controlled by a key that retracts the latch momentarily.

For more functions and information, go to

Tim O’Leary is an experienced security consultant and a regular contributor to Locksmith Ledger.

About the Author

Tim O'Leary

Tim O'Leary is a security consultant, trainer and technician who has also been writing articles on all areas of locksmithing & physical security for many years.