Burglar alarms work by using electrical circuits and sensors to detect intruders. There are types of burglar alarms including motion detectors, which identify changes in position in a specific area, and smoke or fire alarms, which detect possible arson. There are also panic detectors which detect movement changes in a particular area.
A basic burglar alarm contains an electric circuit connected into an entryway, with a switch that opens or closes the circuit. The switch detects acts of intrusion such as opening a window or door. This kind of alarm is built into an entryway. It is classified into two categories. The first is an open-circuit system, in which the circuit is closed and electricity flows when the door is opened. Completion of the circuit triggers the alarm. The second type is a closed-circuit system, wherein the circuit is closed when the door is shut. The circuit opens when someone opens the door, thus triggering an alarm.
In some burglar alarms, sensors are attached to a central unit that sends out a signal upon identifying any intrusion, fire or panic. Signals are typically sent in the form of loud noise. Modern burglar alarms send signals through the Internet or via telephone lines. The homeowner becomes alerted whenever a possible intrusion is identified. Typically, advanced alarm systems send an automated email or phone call to inform a person of any suspicious activity at home.