Keeping intruders out of your home should start with locking the doors and windows. Unfortunately many people cannot even be bothered with this simply step. But because most crimes are crimes of opportunity, often locking the doors can be enough to keep burglars out. For those burglars who are more determined, stronger countermeasures may be needed.
A quality deadbolt with a steel strike plate is a good way to keep a door from being able to be kicked in. A door that can be latched by pulling closed can sometimes be opened by sliding a credit card or other thin, flexible object between the door and the frame. With a deadbolt that is operated solely by a lever or key, this is never possible.
Steel security doors are a good way to provide another level of barrier to the outside world. They often more than double the time required to pick the lock on the front door, and if the thief was planning to kick the door in, they often make this completely impossible. Their location outside the proper front door and their outward-opening mechanism means that kicking the door will not merely tear the deadbolt out of its socket. The door is supported by the entire doorframe, which can probably only knocked in using a police-grade battering ram. Also, banging on steel doors often makes more noise than traditional wooden ones, potentially alerting the neighbors and other passers-by.
A security system is another great line of defense. There are several ways to arm a system. One of the most common is to use a wire and magnet configuration on doors and windows. When the door or window is shut, a magnet keeps an electronic relay activated, but when open, the magnet moves away and allows the alarm to activate. These systems are not foolproof - an electronics-savvy criminal might be able to thwart it by employing a magnet of his own. Furthermore, on windows this method is not as effective because a criminal can break the glass instead of opening the window.
A second method of arming a security system is with sensors that "see" the criminal once entry has been made. These sensors include motion sensors, infrared sensors (that detect body heat), and acoustic sensors (that "hear" the criminal). These sensors can be armed at night or when the family has left the house. While often more effective than door-mounted devices, they have their drawbacks. One such drawback is that they cannot be used in a house with large pets such as dogs or cats, since these animals will trigger the alarm. Also, if a burglar is highly cunning, they can be avoided. For example, a Best Buy was once burglarized by criminals who broke in through the ceiling, and rappelled down to steal goods. Because they never came within 10 feet of the floor, and stayed behind a large sign, they were able to avoid detection by motion sensors.
The most effective system will use multiple lines of defense. A sensor on doors and windows will determine if these portal have been opened, and motion or other sensors inside will catch thieves if they manage to thwart the first line of defense.
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