It is debated whether h aving an alarm system decreases the chances of a burglary. In theory, if a burglar is aware a house has a system, he or she might move on to another home. Even if the alarm system does not keep a burglar from breaking in, the burglar has a tendency to stay a shorter amount of time. This may decrease the number of items stolen and the extent of damage done.
Most systems rely on a combination of contacts placed at doors and windows and motion sensors.
Motion sensors, however, do not detect someone until they are already in the house. Motion sensors should NOT be used as the primary means of detection. It is best that all exterior potential points of entry have contacts that sense when they are open. Glass break sensors are also available and recommended. Additional keypads can be installed.