Alarm Systems

A security alarm is a system designed to detect intrusion – unauthorized entry – into a building or other area. Security alarms are used in residential, commercial, industrial, and military properties for protection against burglary (theft) or property damage, as well as personal protection against intruders. Security alarms in residential areas show a correlation with decreased theft.[1] Car alarms likewise help protect vehicles and their contents. Prisons also use security systems for control of inmates.
Some alarm systems serve a single purpose of burglary protection; combination systems provide both fire and intrusion protection. Intrusion alarm systems may also be combined with closed-circuit television surveillance (CCTV) systems to automatically record the activities of intruders, and may interface to access control systems for electrically locked doors. Systems range from small, self-contained noisemakers, to complicated, multiarea systems with computer monitoring and control. It may even include two-way voice which allows communication between the panel and Monitoring station.

A security alarm is a system designed to detect intrusion – unauthorized entry – into a building or other area. Security alarms are used in residential, commercial, industrial, and military properties for protection against burglary (theft) or property damage, as well as personal protection against intruders. Security alarms in residential areas show a correlation with decreased theft. Car alarms likewise help protect vehicles and their contents. Prisons also use security systems for control of inmates.

Some alarm systems serve a single purpose of burglary protection; combination systems provide both fire and intrusion protection. Intrusion alarm systems may also be combined with closed-circuit television surveillance (CCTV) systems to automatically record the activities of intruders, and may interface to access control systems for electrically locked doors. Systems range from small, self-contained noisemakers, to complicated, multiarea systems with computer monitoring and control. It may even include two-way voice which allows communication between the panel and Monitoring station.

Alarm connection and monitoring

Depending upon the application, the alarm output may be local, remote or a combination. Local alarms do not include monitoring, though may include indoor and/or outdoor sounders (e.g. motorized bell or electronic siren) and lights (e.g. strobe light) which may be useful for signaling an evacuation notice for people during fire alarms, or where one hopes to scare off an amateur burglar quickly. However, with the widespread use of alarm systems (especially in cars), false alarms are very frequent and many urbanites tend to ignore alarms rather than investigating, let alone contacting the necessary authorities. In short, there may be no response at all. In rural areas where nobody may hear the fire bell or burglar siren, lights or sounds may not make much difference, as the nearest emergency responders may arrive too late to avoid losses.

Remote alarm systems are used to connect the control unit to a predetermined monitor of some sort, and they come in many different configurations. High-end systems connect to a central station or first responder (e.g. police/fire/medical) via a direct phone wire, a cellular network, a radio network (i.e. GPRS/GSM), or an IP path. In the case of a dual signaling system two of these options are utilized simultaneously. The alarm monitoring includes not only the sensors, but also the communication transmitter itself. While direct phone circuits are still available in some areas from phone companies, because of their high cost and the advent of dual signaling with its comparatively lower cost they are becoming uncommon. Direct connections are now most usually seen only in federal, state, and local government buildings, or on a school campus that has a dedicated security, police, fire, or emergency medical department (in the UK communication is only possible to an alarm receiving center – communication directly to the emergency services is not permitted).

Wired, wireless, and hybrid systems

Installing a wireless magnetic contact breaker on a door
The trigger signal from every sensor is transmitted to one or more control unit(s) either through wires or wireless means (radio, line carrier, infrared).

Wired system

Convenient when sensors (such as PIRs, smoke detectors, etc.) require external power to operate correctly; however, they may be more costly to install. Entry-level wired systems utilize a star network topology, where the panel is at the center logically, and all devices home run their line wires back to the panel. More complex panels use a Bus network topology where the wire basically is a data loop around the perimeter of the facility, and has drops for the sensor devices which must include a unique device identifier integrated into the sensor device itself (e.g. id. biscuit). Wired systems also have the advantage, if wired properly, of being tamper-evident.

Wireless systems

They often use battery-powered transmitters which are easier to install and have less expensive start-up costs, but may reduce the reliability of the system if the batteries are not maintained. Depending on distance and construction materials, one or more wireless repeaters may be required to get the signal to the alarm panel reliably. A wireless system can be moved to a new home easily, an advantage for those who rent or who move frequently. The more important wireless connection for security is the one between the control panel and the monitoring station. Wireless monitoring of the alarm system protects against a burglar cutting a cable or from failures of an internet provider. This full wireless setup is commonly referred to as 100% wireless.

Hybrid systems

Use both wired and wireless sensors to achieve the benefits of both. Transmitters can also be connected through the premises’ electrical circuits to transmit coded signals to the control unit (line carrier). The control unit usually has a separate channel or zone for burglar and fire sensors, and better systems have a separate zone for every different sensor, as well as internal trouble indicators (mains power loss, low battery, broken wire, etc.).

What does a common home alarm system include?


A typical home alarm system consists of a number of devices placed at doors to a home to detect when the door has been opened. The alarm will sound when the system is activated. Similar contacts are placed on or near windows and will trigger the alarm if the glass is broken to gain entry. The key parts of a home alarm system are:

The control panel. This is the main hub for the system’s wiring. It contains the backup battery, and is where the phone lines are connected if the system is monitored.

The keypad. This allows for arming and disarming the system, usually through input of a numerical code.

The siren. Triggered when the system detects an intruder, it can be visual, aural, or silent sending a signal to the monitoring agency – depending on where the system is installed and whether catching the intruder is a priority.

Motion detectors. These are used to sense changes in a room due to a human presence while the system is armed. Special detectors can be installed in homes that have pets.

Door and window contacts. As mentioned, these sense when a door is opened or a window is opened or broken, and will trigger an alarm if the system is armed.