Door chain

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Door chain

A door chain, security chain, or security door chain consists of a small chain attached to the door frame, which attaches to a track on the door for security purposes. It is a type of lock that is often used along with other types of locks to secure a door.

Uses

Door chains are mainly intended to allow a person inside a structure to open the door slightly for purposes of communicating with individuals outside or exchanging small objects through the door while still preventing the individuals outside from gaining unauthorized access into the structure.

Door chains also can be set in place when the door does not need to be opened. They can only be touched from outside when the door has been opened, and therefore, if the locks on the door are compromised, a door chain may cause some delay, draw more attention, or leave more evidence of force being used when gaining unauthorized access to the structure.

Door chains installed on hollow-core doors, or that are not anchored into solid materials (such as the wood door frame) do not provide protection. This is because the chain can easily be defeated by pushing on a door. The chains are helpful to sound an alert to the person inside that someone is breaking through a door. The noise may be heard by the occupants giving them time to call for help, escape via another exit, or get a weapon to protect themselves. Door chains are also sometimes used to slow down mentally-challenged individuals who may attempt to exit from inside a structure.

Advantages

Door chains are fairly easy to install and use. Use of a door chain provides a little security when dealing with strangers. A properly installed door chain is resistant to tampering from the outside requiring use of physical force to open the door, which will leave obvious evidence.

Disadvantages

Door chains normally come equipped with very short screws which easily rip out. Any amount of force capable of defeating a deadbolt will also defeat a door chain. The tracks are usually straight, and any number of simple tools will allow the chain to be separated from the track. Elderly individuals, uncoordinated people, and individuals with hand tremors may find it difficult to connect the chain to the track. The chain is often a thin metal. Door chains are often installed improperly, making them easily subjected to a number of attacks.

UPVC/PVCU front doors are generally unsuitable for retrofit security devices. Not only is the material not strong enough to support devices fitted with steel screws unless secured into the internal metal framework, but such changes to the original design may invalidate an existing warranty or possibly damage the integral locking assembly.

Improvements

When fitting a standard door chain featuring a linear slide, it is imperative that it not allow the door to open sufficiently for a person's hand to reach through the gap between the door and the doorframe, as otherwise the door chain could be quickly opened from the outside by an intruder.

Alternatives

Security screen doors add a second set of hinges or locks to defeat before access to a structure can be granted. If the intention is to keep thieves out, or keep disturbed individuals in, this is a better solution. Security screen doors also make it possible to open the main door, and communicate with those outside. Some even have mail slots. As an added benefit, security screen doors can allow the door to be opened, and provide for secure ventilation. The main downside is the cost, which is generally about as much as a regular door, and locks are usually sold separately. Installation can also be difficult, as the doorknobs of the two doors may interfere with each other, and the screen material usually interferes with any peephole devices on the door.
A door bar is a newer device intended to replace door chains. It consists of a U shaped bar that attaches to a hinge on the doorframe, and a knob on the door. The bar swings over the knob to restrict the full opening of the door. Door bars are easier to use, and can be made of much sturdier material than door chains. Also, door bars cannot be defeated in the same way that door chains can be, although they can be defeated just as easily in different ways.
Intercoms, peep holes, and mail slots can all serve purposes similar to the door chain when dealing with strangers, and function without opening the door. Of course, these devices do not provide additional protection to the door itself.

References

Locksmithing & Lock picking

Topics	Electric strike Key control Key relevance Lock bumping Lock picking Lockout-tagout Maison key system Rekeying Single-point locking Three-point locking

Components	Bitting Bolt stump Break Interchangeable core Key blank Key code Keyhole Lockset Shear line Split pin

Key types	Berlin key Bump key Change key Master key Skeleton key Smart key Tubular key Transponder key

Mechanical Locks	Bored cylindrical lock Bramah lock Cylinder lock Disc tumbler lock Key retainer Lever tumbler lock (Chubb detector lock) Magnetic-coded lock Magnetic keyed lock Mortise lock Padlock Combination lock Rotary combination lock Time-delay combination locks Pin tumbler lock (snib) Protector lock Relocking device Time lock Tubular pin tumbler lock Warded lock Wafer tumbler lock

Electronic Locks	Electromagnetic lock Electronic lock Electric strike Magnetic-coded lock Keycard lock Electronic/digital-cylinder pin tumbler lock

Specific lock types	Bicycle lock Chamber lock Child safety lock Dead bolt Keycard lock Kensington Security Slot Luggage lock Power door locks The Club TSA lock

Tools	Lockpick Slim Jim Snap gun Tubular lock pick

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Category:Locksmithing Keys Locks Book

This article is issued from Wikipedia - version of the 11/21/2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.