ratio of word probabilities predicted from brain for door and key

door	key
top 10 words in brain distribution (in article): light design material power type build vehicle wood allow common	top 10 words in brain distribution (in article): blade head cut metal century shape modern design form type
top 10 words in brain distribution (not in article): water drink produce lamp plant wine beer tree fruit wheel	top 10 words in brain distribution (not in article): iron steel plant handle hair fruit tool produce nail size
times more probable under door 30 20 10 6 4 2.5 1.25 1 1.25 2.5 4 6 10 20 30 times more probable under key (words not in the model)
A door'" is a moveable barrier used to cover an opening. Doors are used widely and are found in walls or partitions of a building or space, furniture such as cupboards, cages, vehicles, and containers. A door can be opened to give access and closed more or less securely using a combination of latches and locks. (See article Door security). Doors are nearly universal in buildings of all kinds, allowing passage between the inside and outside, and between internal rooms. When open, they admit ventilation and light. The door is used to control the physical atmosphere within a space by enclosing it, excluding air drafts, so that interiors may be more effectively heated or cooled. Doors are significant in preventing the spread of fire. They act as a barrier to noise. (See article Door safety). They are also used to screen areas of a building for aesthetic purposes, keeping formal and utility areas separate. Doors also have an aesthetic role in creating an impression of what lies beyond. Doors are often symbolically endowed with ritual purposes, and the guarding or receiving of the keys to a door, or being granted access to a door can have special significance. Similarly, doors and doorways frequently appear in metaphorical or allegorical situations, literature and the arts, often as a portent of change. Design and construction styles. Many kinds of doors have specific names, depending on their purpose. The most common variety of door consists of a single rigid panel that fills the doorway. Many variations on this basic design are possible, such as "double" doors that have two adjacent independent panels hinged on each side of the doorway. A "'Dutch door'" or "'stable door'" is divided in half horizontally. Traditionally the top half can be opened to allow a horse or other animal to be fed, while the bottom half remained closed to keep the animal inside. "'Saloon doors'" are a pair of lightweight swing doors often found in public bars. Saloon doors, also known as "'cafe doors'", often use "'double action hinges'", which will return the door to the center, regardless of which direction it is opened, due to the double action springs in the doors. Saloon doors that only extend from knee-level to chest-level are known as "'batwing doors'". A "'blind door'" is a door with no visible trim or operable components. It is designed to blend with the adjacent wall in all finishes, and visually to be a part of the wall, a disguised door. A "'barn door'" is a door characteristic of a barn. They are often always found on barns, and because of a barn's immense size (often) doors are subsequently big for utility. A "'French door'", also called a "'French window'", is a door that has multiple windows ("lights") set into it for the full length of the door. Traditional French doors are assembled from individual small pieces of glass and mullions. These doors are also known as true divided lite[sic] French doors. French doors made of double-pane glass (on exterior doors for insulation reasons) may have a decorative grille embedded between the panes, or may also be true divided lite French doors. The decorative grille may also be superimposed on top of single pane of glass in the door. A "'louvred door'" has fixed or movable wooden fins (often called slats or louvers) which permit open ventilation whilst preserving privacy and preventing the passage of light to the interior. Being relatively weak structures, they are most commonly used for wardrobes and drying rooms, where security is of less importance than good ventilation, although a very similar structure is commonly used to form window shutters. A "'flush door'" is a completely smooth door, having plywood or MDF fixed over a light timber frame, the hollow parts of which are often filled with a cardboard core material. Flush doors are most commonly employed in the interior of a dwelling, although slightly more substantial versions are occasionally used as exterior doors, especially within hotels and other buildings containing many independent dwellings. A "'moulded door'" has the same structure as that of flush door. The only difference is that the surface material is a moulded skin made of HDF MDF. It is commonly used as interior doors. A "'ledge and brace door'" is a door made from multiple vertical planks fixed together by two horizontal planks (the ledges) and kept square by a diagonal plank (the brace). A "'wicket door'" is a normal sized door built into a much larger one, such as the gate of a city or castle. A "'bifold door'" id="bifold"/> is a door unit that has several sections, folding in pairs. Wood is the most common material, and doors may also be metal or glass. Bifolds are most commonly made for closets, but may also be used as units between rooms. A "'sliding glass door'", sometimes called an Arcadia door, is a door made of glass that slides open and sometimes has a screen. "'Australian doors'" are a pair of plywood swinging doors often found in Australian public houses. These doors are generally red or brown in color and bear a resemblance to the more formal doors found in other British Colonies' public houses. A "'false door'" is a wall decoration that looks like a door. In ancient Egyptian architecture, this was a common element in a tomb, the false door representing a gate to the afterlife. They can also be found in the funerary architecture of the desert tribes (e.g., Libyan Ghirza). Hinged doors. Most doors are hinged along one side to allow the door to pivot away from the doorway in one direction but not in the other. The axis of rotation is usually vertical. In some cases, such as hinged garage doors often horizontal, above the door opening. Doors can be hinged so that the axis of rotation is not in the plane of the door to reduce the space required on the side to which the door opens. This requires a mechanism so that the axis of rotation is on the side other than that in which the door opens. This is sometimes the case in trains, such as for the door to the toilet, which opens inward. "'A swing door'" has special hinges that allow it to open either outwards or inwards, and is usually sprung to keep it closed. A "'Mead door'" is a double action pivot door capable of swinging both ways. First introduced by Scott Mead, established in Leicester, England. The Mead door is susceptible to forced entry. Sliding doors. It is often useful to have doors which slide along tracks, often for space or aesthetic considerations. A bypass door"' is a door unit that has two or more sections. The doors can slide in either direction along one axis on parallel overhead tracks, sliding past each other. They are most commonly used in closets, in order to access one side of the closet at a time. The doors in a bypass unit will overlap slightly when viewed from the front, in order not to have a visible gap between them. Doors which slide between two wall panels are called pocket doors'". Sliding glass doors are common in many houses, particularly as an entrance to the backyard. Such doors are also popular for use for the entrances to commercial structures. A "'tambour door'" is made of narrow horizontal slats and "rolls" up and down by sliding along vertical tracks and is typically found in entertainment centres and cabinets. Folding doors. Folding doors have an even number of sections, generally 2 to 4, folding in pairs. The doors can open from either side for one pair, or fold off both sides for two pairs. Rotating doors. A "'revolving door'" normally has four wings leaves that hang on a center shaft and rotate one way about a vertical axis. The door may be motorized, or pushed manually using pushbars. People can walk out of and into the building at the same time. Between the point of access and the point of exit the user walks through an airlock. Revolving doors therefore create a good seal from the outside and help to reduce C and heating costs climate control from the building. This type of door is also often seen as a mark of prestige and glamour for a building and it not unusual for neighbouring buildings to install their own revolving doors when a rival building gets one. A"' butterfly door'" called because of its two "wings". It consists of a double-wide panel with its rotation axle in the centre, effectively creating two separate openings when the door is opened. Butterfly doors are made to rotate open in one direction (usually counterclockwise), and rotate closed in the opposite direction. The door is not equipped with handles, so it is a "push" door. This is for safety, because if it could open in both directions, someone approaching the door might be caught off-guard by someone else opening the other side, thus impacting the first person. Such doors are popular in public transit stations, as it has a large capacity, and when the door is opened, traffic passing in both directions keeps the door open. They are particularly popular in underground subway stations, because they are heavy, and when air currents are created by the movement of trains, the force will be applied to both wings of the door, thus equalizing the force on either side, keeping the door shut. "'French Doors'" derived from an original French design called the casement door, can be created with two out-swinging or in-swinging door panels or two sliding panels or pocket doors. Others. An "'up-and-over'" door is often used in garages. Instead of hinges it has a mechanism, often counterbalanced or sprung, that allows it to be lifted so that it rests horizontally above the opening. Also known as an "'overhead'" door. "'Automatic doors'" are powered open and closed either by power, spring, or both. There are several methods by which an automatic door is activated: In addition to activation sensors automatic doors are generally fitted with safety sensors. These are usually an infrared curtain or beam, but can be a pressure mat fitted on the swing side of the door. The purpose of the safety sensor is to prevent the door from colliding with an object in its path by stopping or slowing its motion. "'Inward opening doors'" are doors that can only be opened (or forced open) from outside a building. Such doors pose a substantial fire risk to occupants of occupied buildings when they are locked. As such doors can only be forced open from the outside, building occupants would be prevented from escaping. In commercial and retail situations manufacturers have included in the design a mechanism that allows an inward opening door to be pushed open outwards in the event of an emergency (which is often a regulatory requirement). This is known as a 'breakaway' feature. Pushing the door outward at its closed position, through a switch mechanism, disconnects power to the latch and allows the door to swing outward. Upon returning the door to the closed position, power is restored. Applications. Doors have numerous general and specialized uses in buildings, storage devices, vehicles, etc. In building interiors, doors are generally used to separate interior spaces, rooms, closets, etc. for privacy, convenience, and safety reasons. Doors are also used to secure passages into a building from the exterior for reasons of safety and climate control. Other than these common usages, doors also have the following applications: Doorway. When framed in wood for snug fitting of a door, the doorway consists of two vertical "jambs" on either side, a "lintel" or "head jamb" at the top, and perhaps a "threshold" at the bottom. When a door has more than one movable section, one of the sections may be called a "leaf". See door furniture for a discussion of attachments to doors such as door handles and doorknobs. Related hardware. Door furniture or hardware refers to any of the items that are attached to a door or a drawer to enhance its functionality or appearance. This includes items such as hinges, handles, door stops, etc. Door construction. Panel doors'" (doors built with frame and panel construction, also called "'stile and rail doors'"): "'Plank and batten doors'", (an older design consisting primarily of vertical slats): "'Ledged and braced doors'" Consists of vertical tongue and grooved boards held together with battens and diagonal braces. "'Frame and filled door'" Consists of a solid timber frame, filled on one face, face with Tongue and Grooved boards. Quite often used externally with the boards on the weather face. "'Flush doors'" (many modern doors, including most interior doors): Door swings, or handing, are always determined from the secure side of the door (ie. the side you use the key on, outside to inside, or public to private). Sizing: A standard US door size 36" x 80" (0.91 m x 2.03 m). Note: In Australia, this is different. The fridge rule applies (you can't stand in a fridge, the door always opens towards you). If the hinges are on the left then its a left hand (or left hung) door. If the hinges are on the right then its a right hand (or right hung) door. See the Australian Standards for Installation of Timber Doorsets, AS 1909-1984 pg 6. History. The earliest records are those represented in the paintings of the Egyptian tombs, in which they are shown as single or double doors, each in a single piece of wood. In Egypt, where the climate is intensely dry, there would be no fear of their warping, but in other countries it would be necessary to frame them, which according to Vitruvius (iv. 6.) was done with stiles (sea si) and rails "(see: Frame and panel)": the spaces enclosed being filled with panels (tympana) let into grooves made in the stiles and rails. The stiles were the vertical boards, one of which, tenoned or hinged, is known as the hanging stile, the other as the middle or meeting stile. The horizontal cross pieces are the top rail, bottom rail, and middle or intermediate rails. The most ancient doors were in timber, those made for King Solomon's temple being in olive wood (I Kings vi. 31-35), which were carved and overlaid with gold. The doors dwelt upon in Homer would appear to have been cased in silver or brass. Besides Olive wood, elm, cedar, oak and cypress were used. All ancient doors were hung by pivots at the top and bottom of the hanging stile which worked in sockets in the lintel and sill, the latter being always in some hard stone such as basalt or granite. Those found at Nippur by Dr. Hilprecht, dating from 2000 B.C. were in dolerite. The tenons of the gates at Balawat were sheathed with bronze (now in the British Museum). These doors or gates were hung in two leaves, each about wide and. high; they were encased with bronze bands or strips, 10 in. high, covered with repouss decoration of figures, etc. The wood doors would seem to have been about 3 in. thick, but the hanging stile was over diameter. Other sheathings of various sizes in bronze have been found, which proves this to have been the universal method adopted to protect the wood pivots. In the Hauran in Syria, where timber is scarce the doors were made in stone, and one measuring by is in the British Museum; the band on the meeting stile shows that it was one of the leaves of a double door. At Kuffeir near Bostra in Syria, Burckhardt found stone doors, 9 to. high, being the entrance doors of the town. In Etruria many stone doors are referred to by Dennis. The ancient Greek and Roman doors were either single doors, double doors, sliding doors or folding doors, in the last case the leaves were hinged and folded back. In Eumachia, is a painting of a door with three leaves. In the tomb of Theron at Agrigentum there is a single four-panel door carved in stone. In the Blundell collection is a bas-relief of a temple with double doors, each leaf with five panels. Among existing examples, the bronze doors in the church of SS. Cosmas and Damiano, in Rome, are important examples of Roman metal work of the best period; they are in two leaves, each with two panels, and are framed in bronze. Those of the Pantheon are similar in design, with narrow horizontal panels in addition, at the top, bottom and middle. Two other bronze doors of the Roman period are in the Lateran Basilica. Heron of Alexandria created the earliest known automatic door in the 1st century AD during the era of Roman Egypt. The first foot-sensor-activated automatic door was made in China during the reign of Emperor Yang of Sui (r. 604–618), who had one installed for his royal library. The first automatic gate operators were later created in 1206 by the Arabic inventor, Al-Jazari. The doors of the church of the Nativity at Bethlehem (6th century) are covered with plates of bronze, cut out in patterns: those of Hagia Sophia at Constantinople, of the 8th and 9th century, are wrought in bronze, and the west doors of the cathedral of Aix-la-Chapelle (9th century), of	A key'" is a device which is used to open a lock. A typical key consist of two parts: the "blade", which slides into the keyway of the lock and distinguishes between different keys, and the "bow", which is left protruding so that torque can be applied by the user. The blade is usually designed to open one specific lock, although master keys are designed to open sets of similar locks. Keys provide an inexpensive, though imperfect, method of authentication for access to properties like buildings and vehicles. As such, keys are an essential feature of modern living in the developed world, aing adorned by key fobs and known as a keychain. House keys. A house key'" is the most common sort of key. There are two main forms. The older form is for lever locks, where a pack of flat levers (typically between two and five) are raised to different heights by the key whereupon the slots or "'gates'" of the levers line up and permit a bolt to move back and forth, opening or closing the lock. The teeth or "'bittings'" of the key have flat tops rather than being pointed. Lever lock keys tend to be bigger and less convenient for carrying, although lever locks tend to be more secure. These are still common in, for example, many European countries. The more recent form is that for a pin tumbler cylinder lock. When held upright as if to open a door, a series of grooves on either side of the key (the key's "'profile'") limits the type of lock cylinder the key can slide into. As the key slides into the lock, a series of pointed teeth and notches allow pins to move up and down until those pins are in line with the shear line of the cylinder, allowing that cylinder to rotate freely inside the lock and the lock to open. These predominate in, for example, the United States of America. Car key. A "'car key'" or an "'automobile key'" is a key used to open and or start an automobile, often identified with the logo of the car company at the head. Modern key designs are usually symmetrical, and some use grooves on both sides, rather than a cut edge, to actuate the lock. It has multiple uses for the automobile with which it was sold. A car key can open the doors, as well as start the ignition, open the glove compartment and also open the trunk (boot) of the car. Some cars come with an additional key known as a "'valet key'" that starts the ignition and opens the drivers side door but prevents the valet from gaining access to valuables that are located in the trunk or the glove box. Some valet keys, particularly those to high-performance vehicles, go so far as to restrict the engine's power output to prevent joyriding. Recently, features such as coded immobilizers have been implemented in newer vehicles. More sophisticated systems make ignition dependent on electronic devices, rather than the mechanical keyswitch. Ignition switches locks are combined with security locking of the steering column (in many modern vehicles) or the gear lever (Saab Automobile). In the latter, the switch is between the seats, preventing damage to the driver's knee in the event of a collision. Keyless entry systems, which utilize either a door-mounted keypad or a remote control in place of a car key, are becoming a standard feature on many new cars. Some of them are handsfree. Some keys are high-tech in order to prevent the theft of a car. Mercedes-Benz uses a key that, rather than have a cut metal piece to start the car, uses an encoded infrared beam that communicates with the car's computer. If the codes match, the car can be started. These keys can be expensive to replace, if lost, and can cost up to US$400. Some car manufacturers like Land Rover and Volkswagen use a 'switchblade' key where the key is spring-loaded out of the fob when a button is pressed. This eliminates the need for a separate key fob. This type of key has also been known to be confiscated by airport security officials. Master key. A "'master key'" is intended to open a set of several locks. Usually, there is nothing special about the key itself, but rather the locks into which it will fit. These locks also have keys which are specific to each one (the "'change key'") and cannot open any of the others in the set. Locks which have master keys have a second set of the mechanism used to open them which is identical to all of the others in the set of locks. For example, master keyed pin tumbler locks will have two shear points at each pin position, one for the change key and one for the master key. A far more secure (and more expensive) system has two cylinders in each lock, one for the change key and one for the master key. Larger organizations, with more complex "grandmaster key" systems, may have several masterkey systems where the top level grandmaster key works in all of the locks in the system. A practical attack exists to create a working master key for an entire system given only access to a single master-keyed lock, its associated change key, a supply of appropriate key blanks, and the ability to cut new keys. This is described in Locksmiths may also determine cuts for a replacement master key, when given several different key examples from a given system. Control key. A "'control key'" is a special key used in removable core locking systems. The control key enables a user with very little skill to remove from the cylinder, quickly and easily, a core with a specific combination and replace it with a core with a different combination. In Small Format Interchangeable Cores (SFIC), similar to those developed by Frank Best of the Best Lock Corporation, the key operates a separate shear line, located above the operating key shear line. In Large Format Removable Cores, the key may operate a separate shear line or the key may work like a master key along the operating shear line and also contact a separate locking pin that holds the core in the cylinder. SFIC's are interchangeable from one brand to another, while LFRC's are not. Double-sided key. A "'double-sided key'" is very similar to a house or car key with the exception that it has two sets of teeth, an upper level standard set of teeth and a lower, less defined set of teeth beside it. This makes the double-sided key's profile and its corresponding lock look very similar to a standard key while making the attempt to pick the lock more difficult. As the name implies, this type of key has four sides, making it not only harder to duplicate and the lock harder to pick, but it is also physically more durable. Paracentric key. A "'paracentric key'" is designed to open a paracentric lock. It is distinguishable by the contorted shape of its blade, which protrudes past the centre vertical line of the key barrel. Instead of the wards on the outer face of the lock simply protruding into the shape of the key along the spine, the wards protrude into the shape of the key along the entire width of the key, including along the length of the teeth. Patented by the Yale lock company in 1898, paracentric cylinders are not exceptionally difficult to pick, but require some skill and know-how on the part of the person attempting to pick the lock. Skeleton key=== A "'skeleton key'" (or "'passkey'") is a very simple design of key which usually has a cylindrical shaft (sometimes called a "shank") and a single, minimal flat, rectangular tooth or "bit". Skeleton keys are also usually distinguished by their "bow", or the part one would grasp when inserting the key, which can be either very plain or extremely ornate. A skeleton key is designed to circumvent the wards in warded locks. Warded locks and their keys provide minimal security and only a slight deterrent as any key with a shaft and tooth that has the same or smaller dimensions will open the lock. However, warded keys were designed to only fit a matching lock and the skeleton key would often fit many. Many other objects which can fit into the lock may also be able to open it. Due to its limited usefulness, this type of lock fell out of use after more complicated types became easier to manufacture. In modern usage, the term "skeleton key" is often misapplied to ordinary bit keys and barrel keys, rather than the correct definition: a key, usually with minimal features, which can open all or most of a type of badly designed lock. Bit keys and barrel keys can be newly-minted (and sold by restoration hardware companies) or antiques. They were most popular in the late 1800s, although they continued to be used well into the 20th century and can still be found today in use, albeit in vintage homes and antique furniture. A bit key is distinguished from a barrel key in that a bit key usually has a solid shank, whereas a barrel shafted key can be made either by drilling out the shank from the bit end or by folding metal into a barrel shape when forging the key. Tubular key. A tubular key'" (sometimes referred to as a "barrel key" when describing a vintage or antique model) is one that is designed to open a tubular pin tumbler lock. It has a hollow, cylindrical shaft which is usually much shorter and has a larger diameter than most conventional keys. Antique or vintage-style barrel keys often closely resemble the more traditional "skeleton key" but are a more recent innovation in keymaking. In modern keys of this type, a number of grooves of varying length are built into the outer surface at the end of the shaft. These grooves are parallel to the shaft and allow the pins in the lock to slide to the end of the groove. A small tab on the outer surface of the shaft prevents the pins in the lock from pushing the key out and works with the hollow center to guide the key as it is turned. The modern version of this type of key is harder to duplicate as it is less common and requires a different machine from regular keys. These keys are most often seen in home alarm systems and bicycle locks, in the United States. Zeiss key. A Zeiss key'" (also known as a "'Cruciform key'") is a cross between a house key and a tubular key. It has three sets of teeth at 90 degrees to each other with a flattened fourth side. Though this type of key is easy to duplicate, the extra sets of teeth deter lockpicking attempts. Do Not Duplicate key. A "'Do Not Duplicate key'" (or "'DND key'", for short) is one which has been stamped "do not duplicate" and or "duplication prohibited" or similar by a locksmith or manufacturer as a passive deterrent to prevent a retail key cutting service from duplicating a key without authorization or without contacting the locksmith or manufacturer who originally cut the key. More importantly, this is an access control system for the owner of the key, such as a maintenance person or security guard, to identify keys that should not be freely distributed or used without authorization. Though it is intended to prevent unauthorized key duplication, copying restricted keys remains a common security problem. There is no direct legal implication in the US for someone who copies a key that is stamped "do not duplicate" (unless it is a government owned key), but there are patent restrictions on some key designs (see "restricted keys"). The Associated Locksmiths of America calls DND keys "not effective security", and "deceptive because it provides a false sense of security." United States Code deals with United States Post Office keys, and deals with United States Department of Defense keys. Restricted key. A restricted keyblank'" is a keyway and blank for which a manufacturer has set up a restricted level of sales and distribution. Restricted keys are often protected by patent, which prohibits other manufacturers from making unauthorized productions of the key blank. In many jurisdictions, customers must provide proof of ID before a locksmith will duplicate a key using a restricted blank. These days, many restricted keys have special in-laid features, such as magnets, different types of metal, or even small computer chips to prevent duplication. Keycard. A "'keycard'", while not actually considered a key, is a plastic card which stores a digital signature that is used with electronic access control locks. It is normally a flat, rectangular piece of plastic and may also serve as an ID card. There are several popular type of keycards in use and include the mechanical holecard, bar code, magnetic stripe, smart card (embedded with a read write electronic microchip), and RFID proximity cards. The keycard is used by presenting it to a card reader; swiping or inserting of mag stripe cards, or in the case of RFID cards, merely being brought into close proximity to a sensor. Bar code technology is not a secure form of a key, as the bar code can be copied in a photocopier and often read by the optical reader. Magnetic stripe keycards are becoming increasingly easy to copy, but have the security advantage that one may change the stored key in a magnetic swipe card in case the current key may be compromised. This immediate change of the "key" information can be applied to other media, but this media probably offers the least expensive option, and the most convenient to users and managers of systems that use this media. Example: If you own a car with this system, you can change your keys anytime you want. You can buy new media anywhere a gift card is sold. At least at this point in time, you could buy a gift card for a penny, then use that as the media for the keys to your car. If the system uses digital environmental data samples to create the "key" string, every car can have a set of keys that no one else has. If a card is stolen, or copied without authorization, the card can be remade, and the car security system can be synchronized with the new card, and no longer activationally responsive to the copy of the old card. This approach can empower the system controller (owner individual or centralized administration of a business). Computerized authentication systems, such as key cards, raise privacy concerns, since they enable computer surveillance of each entry. Currently RFID cards and key fobs are becoming more and more popular due to its ease of use. Many modern households have installed digital locks that make use of key cards, in combination with biometric fingerprint and keypad PIN options. The first keycard was the mechanical holecard type patented by Tor Sørnes, a concept he later developed into the magnetic stripe card key. History of locks and keys. Wooden locks and keys were in use as early as 4,000 years ago in Egypt. It is also said that key was invented by Theodore of Samos in the 6th century BC. In the United States, keys have been seen as a symbol of power since colonial times. When William Penn arrived in Delaware 1682, a very elaborate ceremony was carried out where he was given the key to the defense works. Flat metal keys proliferated in the early 20th century, following the introduction of mechanical key duplicators, which allow easy duplication of such keys. Key duplication. "'Key cutting (after cutting, the metalworking term for "shaping by removing material") is the primary method of key duplication: a flat key is fitted into a vise grip in a machine, with a blank attached to a parallel vise grip, and the original key is moved along a guide, while the blank is moved against a wheel, which cuts it. After cutting, the new key is deburred: scrubbed with a metal brush to remove burrs, small pieces of metal remaining on the key, which, were they not removed, would be dangerously sharp and, further, foul locks. Different key cutting machines are more or less automated, using different milling or grinding equipment, and follow the design of early 20th century key duplicators. Key duplication is available in many retail hardware stores and of course as a service of the specialized locksmith, though the correct key blank may not be available. Certain keys are designed to be difficult to copy, for access control, such as Medeco, while others are simply stamped Do Not Duplicate to advise that access control is requested, but in the US, this disclaimer has no legal weight. History of key duplication. A machine permitting rapid duplication of flat metal keys, which contributed to the proliferation of their use during the 20th century, may have been first invented in the United States in 1917 (image to the left): Keys in Heraldry. Keys appear in various symbols and coats of arms, the most well-known being that of the Vatican- derived from the story of Saint Peter, the first Pope, being given the Keys of Heaven.