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 security restrictor, aka a door swing bar lock, 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. 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. A disadvantage to door bar installation is that the door must be level with the wall, so the lock cannot be used if the home has trim that projects from the wall. 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 http://www.cityofpaloalto.org/depts/pol/news/details.asp?NewsID=259&TargetID=95 http://www.dorset.police.uk/pdf/stop-chain-check2.pdf Chains Door furniture Locks (security device)