An electronic lock (more precisely an electric lock) is a locking device which operates by means of electric current. Electric locks are sometimes stand-alone with an electronic control assembly mounted directly to the lock. More often electric locks are connected to an access control system. The advantages of an electric lock connected to an access control system include: key control, where keys can be added and removed without re-keying the lock cylinder; fine access control, where time and place are factors; and transaction logging, where activity is recorded.
Electric locks use magnets, solenoids, or motors to actuate the lock by either supplying or removing power. Operating the lock can be as simple as using a switch, for example an apartment intercom door release, or as complex as a biometric based access control system.
Types of electric locks
The most basic type of electronic lock is a magnetic lock (commonly called a mag lock). A large electro-magnet is mounted on the door frame and a corresponding armature is mounted on the door. When the magnet is powered and the door is closed, the armature is held fast to the magnet. Mag locks are simple to install and are very attack resistant. One drawback is that improperly installed or maintained mag locks can fall on people. and also that one must unlock the mag lock to both enter and leave. This has caused fire marshals to impose strict codes on the use of mag locks and the access control practice in general. Additionally, NFPA 101, Standard for Life Safety and Security, as well as the ADA (Americans with Disability Act) require "no prior knowledge" and "one simple movement" to allow "free egress". This means that a person must be able to walk up to a door and with one motion (no push buttons, or having another person unlock the door, or read a sign "special knowledge") and exit. Other problems include a lag time (delay) in releasing as the collapsing magnetic field is not instantaneous. This lag time can cause a user to walk into the door. Finally, mag locks by design fail unlocked, that is if power is removed they unlock. This could be a problem where security is a prime concern. Additionally, power outages could affect mag locks installed on fire listed doors, which are required to remain latched at all times. Thus, a mag lock would not meet current fire codes as the primary means of securing a fire listed door to a frame. Because of this, many commercial doors (this typically does not apply to private residences) are moving over to stand alone locks, or electric locks installed under a Certified Personnel Program. The first mechanical recodable card lock was invented in 1976 by Tor Sørnes, who had worked for VingCard since the 1950s. The first card lock order was shipped in 1979 to Westin Peachtree Plaza Hotel, Atlanta, USA. This product triggered the evolution of electronic locks for the hospitality industry.
Electric strikes (also called electric latch release) replace a standard strike mounted on the door frame and receive the latch and latch bolt. Electric strikes can be simple to install when they are designed for drop-in replacement of a standard strike, although some electric strikes require that the door frame be heavily modified. Installation of a strike into a Fire Listed Door (for open backed strikes on pairs of doors) or Frame must be done under listing agency authority if any modifications to the frame are required (mostly for commercial doors and frames). Since there is no current Certified Personnel Program to allow field installation of electric strikes into fire listed door openings, listing agency field evaluations would most likely require the door and frame to be de-listed and replaced. Electric strikes allow mechanical free egress: As a user leaves, he operates the lockset in the door, not the electric strike in the door frame. Electric strikes can also be either fail unlocked (except in Fire Listed Doors, as they must remain latched when power is not present), as a mag lock, or the more secure fail locked. Electric strikes are easier to attack than a mag lock. It is simple to lever the door open at the strike, as often there is an increased gap between the strike and the door latch. Latch guards are often used to cover this gap.
Electric mortise and cylindrical locks are drop in replacements for the door mounted mechanical locks. A hole must be drilled in the door for electric power wires. Also a power transfer hinge is used to get the power from the door frame to the door. Electric mortise and cylindrical locks allow mechanical free egress. Electric mortise and cylindrical locks can be either fail unlocked or fail locked. In the US, UL rated doors must retain their rating. In new construction doors are cored and then rated. In retofits, the doors must be re-rated.
Electrified exit hardware, sometimes called panic hardware or crash bars, are used in fire exit applications. One pushes against the bar to open it, making it the easiest of mechanically free exit methods. Electrified exit hardware can be either fail unlocked or fail locked. A drawback of electrified exit hardware is their complexity which requires skill to install and maintenance to assure proper function. Only hardware labeled "Fire Exit Hardware" can be installed on fire listed doors and frames and must meet both Panic Exit listing Standards and Fire listing Standards.
Motor operated locks are used throughout Europe. A European motor operated lock has two modes, day mode where only the latch is electrically operated, and night mode where the more secure deadbolt is electrically operated.
Electronic locks offer a variety of means of authentication; those described below are not considered exhaustive.
Numerical codes, passwords and passphrases
Perhaps the most prevalent form of electronic lock is that using a numerical code for authentication; the correct code must be entered in order for the lock to deactivate. Such locks typically provide a keypad, and some feature an audible response to each press. Combination lengths are usually between 4 and 6 digits long.
Another means of authenticating users is to require them to scan or "swipe" a security token such as a smart card or similar, or to interact a token with the lock. For example, some locks can access stored credentials on a personal digital assistant (PDA) using infrared data transfer methods.
As biometrics become more and more prominent as a recognized means of positive identification, their use in security systems increases. Some new electronic locks take advantage of technologies such as fingerprint scanning, retinal scanning and iris scanning, and voiceprint identification to authenticate users.
Radio-frequency identification (RFID) is the use of an object (typically referred to as an RFID tag) applied to or incorporated into a product, animal, or person for the purpose of identification and tracking using radio waves. Some tags can be read from several meters away and beyond the line of sight of the reader. This technology is also used in modern electronic locks.
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