lock and key

lock and key,

fastening fitted to an entryway, such as a gate or door, or a container, such as a cabinet, drawer or safe, to keep it closed and/or prevent unauthorized access or use. Locks typically consist of a sliding, pivoted, or rotary bolt protected by a fixed or movable object. A lock may be opened by a mechanical, magnetic, electric, electronic, or electromechanical key or by employing a code or sequence of numbers or letters.

Mechanical Locks

There are two basic types of mechanical locks, each with variations. The oldest and simplest is the warded lock, which is essentially a spring-loaded bolt in which a notch has been cut. The key fits into the notch and slides the bolt backward and forward. The lock takes its name from the fixed projections, or wards, inside the lock and around the keyhole. The correct key has notches cut into it that match the wards, which block the wrong key from operating the lock. The ward lock is the easiest to pick and now is used only for cheap padlocks.

The tumbler lock contains one or more pieces of metal (called tumblers, levers, or latches) that fall into a slot in the bolt and prevent it being moved. The proper key has serrations that raise the metal pieces to the correct height above the slot, allowing the bolt to slide. There are three types of tumbler locks, pin-tumbler, disk-tumbler, and lever-tumbler. Pin-tumbler locks are the most common. The tumblers in this type of lock are small pins. The modern door lock is a compact pin-tumbler cylinder lock of the type developed (1860) by the American inventor Linus Yale. Door locks on automobiles and most high-security locks have pin tumblers. Disk- or wafer-tumbler locks, use flat disks, or wafers, instead of pins. When the proper key is inserted, the disks retract, releasing the bolt. Disk-tumbler locks are often used in desks and file cabinets. Lever-tumbler locks employ a series of different-sized levers resting on a bolt pin to prevent the bolt from moving. When the proper key is inserted, all the levers are raised to the same height, enabling the bolt pin to release the bolt. Lever-tumbler locks are often used in briefcases, safe-deposit boxes, and lockers.

The first of the keyless locks was the combination lock, developed at the beginning of the 17th cent. In it a number of rings inscribed with letters or numbers are threaded on a spindle. To open the lock the rings must be turned to form a code word or number, which causes the slots inside the rings to align and permits the spindle to be drawn out. A variant of the combination lock employs a movable dial with a series of numbers around it in place of the rings. The dial must be turned clockwise and counterclockwise in the proper sequence of numbers to align disk tumblers and open the lock. Once used only for padlocks, combination locks began to be used in safes and strong-room doors during the last half of the 19th cent. The time lock, first used successfully c.1875, has a clock mechanism that is set to permit opening only a certain time.

Electric and Magnetic Locks

Recent lock developments include the magnetic-key lock, in which the pins are actuated by small magnets on the key, which has no serrations. When the key is inserted into the lock, these magnets repel magnetized spring-loaded pins, raising them in the same way that the serrations on a tumbler-type key would. The card-key lock is actuated by a series of magnetic charges; the card-key is popular where security is vital, because a new series may be electronically defined for each new user, without having to change the lock itself. Similarly, electronic card access systems are used in many hotels and office buildings. A special "key" system uses a paperboard or plastic card, on which a code is recorded as a series of holes or bumps, or a microchip or a magnetic strip on which a code is stored. A card reader at the lock location reads the code and sends the information to a computer, which sends a signal to release the bolt if the code is correct. Electronic combination locks similarly use a computer to compare a combination stored in memory with one entered on a keypad; access is permitted if the combinations match. In a biometric entry system the numeric keypad is replaced by a scanner, which captures an individual's fingerprint, palmprint, signature, or other personal characteristic and compares it with that in the computer's memory. Biometric entry systems are most often used in high-security areas, such as nuclear power plants.

In an electromagnetic lock a metal plate is attached to the door and an electromagnet is attached to the doorframe opposite the plate. When the current flows, the electromagnet attracts the plate, holding the door closed, When the flow of current is stopped, the door unlocks. A variation places the plate and electromagnet so that the door is held open when current flows, enabling the door to be closed automatically when the current stops.

Keyless entry systems, which are common in motor vehicles, rely on a keychain fob that contains a remote-control unit consisting of an integrated circuit and a radio transmitter. The fob sends a low-powered radio signal to a receiver in the motor vehicle, and, if the received code is the correct one, the receiver in the vehicle relays the signal to a microprocessor, which opens the lock. The acceptance of such entry systems has led to devices that allow additional functions within the vehicle to be activated remotely.

In other keyless entry systems, radio-frequency identificationradio-frequency identification
(RFID), a technology that uses radio waves to transmit data and uniquely identify an animal, person, or thing. An RFID system typically consists of a tag and a reader.
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 (RFID) is used. An RFID tag, card, or fob is brought within range of radio waves produced by an RFID reader or interrogator, allowing data to be exchanged; when the microprocessor controlling the lock confirms that the received data is associated with someone allowed entry, the door is unlocked. RFID systems are more commonly used to control entry into buildings or rooms, and the use of a computer to control locks that use RFID allows access to specific areas to be restricted to specific people or at specific times.

References in classic literature ?
Unknown to all but Hester Prynne, and possessing the lock and key of her silence, he chose to withdraw his name from the roll of mankind, and, as regarded his former ties and interest, to vanish out of life as completely as if he indeed lay at the bottom of the ocean, whither rumour had long ago consigned him.
As for Captain Speedy, he was shut up in his cabin under lock and key, and was uttering loud cries, which signified an anger at once pardonable and excessive.
When both the animals had been safely put under lock and key, he felt that he might breathe more freely.
There's no safety for anyone until he is under lock and key.
He could not forcibly have abducted the missing pair and kept them under lock and key.
Archer sighing, as if it were not such an enviable thing to be in an age when ladies were beginning to flaunt abroad their Paris dresses as soon as they were out of the Custom House, instead of letting them mellow under lock and key, in the manner of Mrs.
Again, therefore, she applied herself to the key, and after moving it in every possible way for some instants with the determined celerity of hope's last effort, the door suddenly yielded to her hand: her heart leaped with exultation at such a victory, and having thrown open each folding door, the second being secured only by bolts of less wonderful construction than the lock, though in that her eye could not discern anything unusual, a double range of small drawers appeared in view, with some larger drawers above and below them; and in the centre, a small door, closed also with a lock and key, secured in all probability a cavity of importance.
Back yonder, an hour's journey from here, we passed through an Arab village of stone dry-goods boxes (they look like that,) where Noah's tomb lies under lock and key.
Do you think yourself my master, that you try to keep me under lock and key like this?
he said, with his mouth full; "they seize a man, some fine day, keep him under lock and key for ten years, and write to you, 'Watch this fellow well,' or 'Keep him very strictly.
I won't tell you how we looked at letters and other things which he forgot to leave under lock and key.
Besides the usual lock and key, it possessed two solid bolts, fastening inside at the top and the bottom.