What is a Door Alarm?
A door alarm is a small electronic device that is programmed to detect when the door to which it is attached has been opened. When that door is opened, an alarm is triggered. There are a number of types of door alarms available, all of which are fairly inexpensive and can be installed without much effort. These alarms have the added benefit of being both wireless and portable as well.
Door security bars
This category of door alarm consists of a metal bar extending across a door from frame to frame, effectively bracing it shut. Once armed, it sets off an alarm if it detects too much pressure being put on the bar (from someone attempting to open the door), frequently deterring the intruder. A security bar’s main drawback is the lack of portability – it does not collapse, and is therefore usually too long to fit into most luggage.
Doorstops
A doorstop is a small, wedge-shaped door alarm device that simply need to be slid under a door to brace it shut. These can also have alarms installed in them that will trigger if too much pressure is applied to the door, discouraging entry by outsiders. Because of their small size, door stops are sometimes not as secure as other options, such as security bars; additionally, some doors may be mounted in such a way that there is not enough room beneath the door to wedge the door stop into place. However, the small size and ease of installation involved make doorstops a good choice for a temporary door alarm until a more effective one can be acquired.
In-door alarms
In-door alarms are designed to hang over a door handle, attaching to the door with prongs that insert themselves between the door and the doorjamb; like many door alarms, these are easy to install and portable, making them excellent for temporary use. They will also set off loud alarms if the door is opened; however, unlike the security bar or doorstop, an in-door alarm will not actually prevent entry to the house or room. This type of door alarm may be rendered useless if there is too much space between the door and the jamb – causing the prongs to dislodge, and either deactivating the alarm or causing a false alarm to be set off. On the other hand, a door alarm of this type is usually versatile enough that it can be used to secure things other than a door, protecting them from theft.