Understanding the Basics of Burglar Alarms

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Home security systems have become increasingly popular in recent years. Burglar alarms are now a standard feature in many businesses and private homes. These systems vary widely, from simple DIY kits to complex professional installations. However, they are all based on the same basic design principles. In this article, we will explore some of these concepts and look at a few specific alarm designs.

Breaking the Circuit

The most basic type of burglar alarm uses a simple electric circuit installed in an entryway. Electricity flows through a circuit only when there is a path between two points of opposing charge. To turn the electricity on or off, a switch must be opened or closed. In a burglar alarm, the switch detects an intruder attempting to gain entry and triggers an alarm.

There are two types of alarm systems: closed-circuit and open-circuit. In a closed-circuit system, the circuit is closed when a door or window is shut, allowing electricity to flow. If an intruder opens the door or window, the circuit is broken, triggering the alarm. In an open-circuit system, opening a door or window completes the circuit, allowing electricity to flow and triggering the alarm.

A magnetic sensor is a simple way to build a closed-circuit system into an entryway. It consists of a battery-powered circuit, a spring-driven metal switch in a door frame, a magnet in the door, and a buzzer with a relay-driven switch. When the door is closed, the magnet aligns with the switch, completing the circuit and keeping the buzzer circuit open. If the magnet moves when the door is opened, the switch snaps open, cutting off the current and activating the alarm.

Another simple burglar alarm uses a small button embedded in the door frame. Closing the door pushes the button in, completing the circuit. When an intruder opens the door, the button is released, breaking the circuit and sounding the alarm.

These designs, which only consist of a battery and buzzer, are not very effective as security systems since a burglar can simply close the door to turn off the buzzer. To improve security, a control box is added to the alarm circuit. The control box has its own power supply and monitors the circuits to trigger the alarm when they are opened or closed. However, the alarm won’t stop until a security code is entered at the connected keypad. The control box is usually located in an inconspicuous place for added security.

Various alarm systems can be created using this concept by turning the burglar’s actions into the circuit switch. For example, the glass window can be made into a circuit by running a current through a thin line of foil wire affixed to its surface. If the glass is broken, the circuit is broken as well, triggering the alarm. Floor mats are another option using an open circuit design with two metal strips spaced apart. When someone steps on the mat, the pressure completes the circuit. These systems are best for guarding the perimeter of a building.

To detect intruders who are already inside the building, a motion detector is needed since their actions are unpredictable. Radar-based motion detectors emit bursts of microwave radio energy or ultrasonic sound waves and monitor the reflection pattern to detect any disturbance. Photo-sensor motion detectors, on the other hand, use two components and sound an alarm signal when someone enters the room.

In a home security system, there are two main components: a source of focused light, such as a laser beam, and a light sensor. These are aimed at each other across a passageway in the house. When someone walks between the two, the path of the beam is briefly blocked, causing a drop in light levels that triggers a signal to the control box. More advanced systems use passive infrared (PIR) motion detectors that detect infrared energy emitted by an intruder’s body heat. The system triggers the alarm only when infrared energy levels change rapidly. The control box can activate a siren, flashing lights, and a telephone auto-dialer to alert the homeowner and police. New and improved burglar alarms are constantly emerging, but they all operate around the same basic structure. To learn more about specific alarm devices and installation techniques, visit relevant websites or consult a security system installer in your area.

Additional Information

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Useful Links

  • Visit The National Burglar & Fire Alarm Association’s Website
  • Get Your Installed Burglar Alarm System Certified
  • Create Your Own Burglar Alarm with These Simple Steps
  • Learn About Oakland’s Burglar Alarm Ordinance
  • Orlando Police Department’s Guide to Buying an Alarm System


1. What is a burglar alarm?

A burglar alarm is a system designed to detect unauthorized entry into a building or area and alert the owner or security personnel. It typically consists of sensors, a control panel, and an alarm sounder.

2. How do sensors in a burglar alarm work?

The sensors in a burglar alarm are designed to detect movement, heat, or sound. When triggered, they send a signal to the control panel, which activates the alarm sounder. Some alarm systems also have cameras that can capture footage of the intruder.

3. What are the types of burglar alarms?

There are several types of burglar alarms, including wired alarms, wireless alarms, and hybrid alarms. Wired alarms are connected by cables and are often used in larger buildings. Wireless alarms are easier to install and are often used in smaller homes. Hybrid alarms combine wired and wireless components.

4. How does a control panel in a burglar alarm work?

The control panel is the brain of the burglar alarm system. It receives signals from the sensors and decides whether to activate the alarm sounder. It also has a battery backup in case of a power outage.

5. Do burglar alarms need to be monitored?

While burglar alarms can be set to sound an alarm when triggered, they are often monitored by a security company. If the alarm is triggered, the security company is alerted and can dispatch police or security personnel to investigate.

6. What are the benefits of installing a burglar alarm?

Installing a burglar alarm can provide peace of mind and help deter burglars. It can also reduce the risk of property damage or loss and lower insurance premiums.

7. What factors should be considered when choosing a burglar alarm system?

When choosing a burglar alarm system, consider factors such as the size of the property, the level of security required, and budget. It’s also important to choose a reputable installer and ensure the system meets industry standards.

8. Can a burglar alarm be integrated with other security systems?

Yes, many burglar alarm systems can be integrated with other security systems such as CCTV cameras, access control systems, and fire alarms. This provides a more comprehensive security solution and allows for centralized monitoring and control.

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