The door chain , security chain , or security door chain consists of a small chain attached to the door frame, attached to a track on the door for security purposes. This is a type of key that is often used along with other key types to secure the door.
Video Door chain
Usage
The door chain is primarily intended to allow a person inside the structure to open the door slightly for the purpose of communicating with the individual outside or exchanging small objects through the door while still preventing the outside individual from gaining unauthorized access into the structure.
The door chain can also be installed when the door does not need to be opened. They can only be touched from the outside when the door has been opened, and therefore, if the lock on the door is compromised, the door chain may cause some delays, attract more attention, or leave more evidence of the power used when gaining unauthorized access to the structure.
The door chain attached to the hollow-core door, or which does not dock into solid materials (such as wooden door frames) does not provide protection. This is because the chain can be easily defeated by pushing the door. The chain is useful to alert the person inside that someone is breaking through the door. The noise may be heard by the occupants giving them time to ask for help, escaping through another way, or getting weapons to protect themselves. Door chains are also sometimes used to slow down individuals who experience mental disorders that may be trying to get out of the structure.
Maps Door chain
Profit
The door chain is quite easy to install and use. The use of door chains provides little security when dealing with strangers. Properly fitted door chains are resistant to outside interference requiring the use of physical force to open doors, which will leave clear evidence.
Disadvantages
The door chain is usually equipped with very short screws that easily fall out. A number of forces capable of defeating deadbolts will also defeat the door chain. Tracks are usually straight, and a number of simple tools will allow the chain to be separated from the track. Parents, uncoordinated people, and individuals with hand shakes may find it difficult to connect chains to a track. The chain is often a thin metal. The door chain is often installed incorrectly, making it vulnerable to a number of attacks.
The UPVC/PVCU front door is generally not suitable for retrofit security devices. Not only are materials not strong enough to support devices equipped with steel screws unless secured into an internal metal frame, but such changes to the original design may void the existing warranty or may damage the integral locking unit.
Repair
- When installing a standard door chain featuring linear slides, it is important that it does not allow the door to open enough for a person's hand to reach through the gap between the door and the door frame, because otherwise the door chain can be quickly opened from the outside by intruders.
Alternative
- The security screen door adds a second set or key to be defeated before access to the structure can be granted. If the goal is to drive away thieves, or continue to harass individuals, this is a better solution. The security screen door also allows to open the main door, and communicate with the outside. Some even have mail slots. As an added benefit, security screen doors can allow doors to open, and provide safe ventilation. The main drawback is the cost, which is generally almost the same as the regular door, and the lock is usually sold separately. Installation can also be difficult, as both door handles can interfere with each other, and screen material usually disrupts the peephole device in the door.
- The door bar is a new device intended to replace the door chain. It consists of a U-shaped bar that attaches to the hinges on the door frame, and the door knob. The blade swings over the button to limit the full opening of the door. The door bar is easier to use, and can be made of a much more robust material than a door chain. Also, the doorstop can not be defeated in the same way as door chains, though they can be easily defeated in different ways.
- The intercoms, peephole and letter slots can all serve a purpose similar to a door chain when faced with a stranger, and function without opening the door. Of course, this device does not provide additional protection to the door itself.
References
- http://www.cityofpaloalto.org/depts/pol/news/details.asp?NewsID=259&TargetID=95
- http://www.dorset.police.uk/pdf/stop-chain-check2.pdf
Source of the article : Wikipedia
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