Door chain
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A door chain is a security device that is mainly used on entrance doors (of single-family houses or apartments in multi-family houses). The simplest and long-established variant consists of a chain that is attached to the door frame and a rail that is located on the door. This bar is open at one end, closed at the other, and there is a special hook on the chain that can be pushed into the open end of the bar. The rail is usually screwed on horizontally so that the chain can only be hooked when the door is closed. If you then open the door, the hook slides to the closed end of the rail. This means that the door can only be opened a little, depending on the length of the chain. Then you can talk to a visitor without them having to push the door open and get into the apartment without authorization. If you want to let him in, the door must first be closed in order to be able to unhook the chain, so it is of no use to an intrusive visitor to put his foot in the gap and thus keep the door open. Small objects can also be exchanged or viewed through the door gap, e.g. B. an ID that proves the identity of the visitor and possibly also his authorization.
However, the fact that it cannot be opened from the outside is also a disadvantage of the classic door chain. Has z. For example, if a person in the apartment presents the door chain and then gets into a helpless situation in which they can no longer open the chain, the chain must be destroyed by helpers. Modern models therefore consist of a chain that is permanently attached to the door and hooked into a snap lock on the frame. This lock is mostly partially rotatable and can therefore be opened both from the inside and outside with a key. So you can show the door chain when you leave the apartment, and opening from the outside (provided a key is available) is also possible. Some versions combine the rail and the lock, so the door chain can be presented and opened from the inside without a key.
In addition, models are offered in which the chain is simply hung over the door handle , so that drilling into the door is not necessary. Door chains are also available with an electronic alarm device that emits a warning tone in the event of manipulation. Basically, however, the stability of door chains is less than that of a locking bracket on an additional lock. Above all, the fastenings on the door and wall are sometimes weak points that can give way when the appropriate force is used.
