Intruder Alarm

An Intruder Alarm is a system designed to detect intrusion, such as unauthorised entry, into a building or other areas such as a home or school. Security alarms used in residential, commercial and industrial properties protect against burglary  or property damage, as well as personal protection against intruders.

Some alarm systems serve a single purpose of burglary protection; combination systems provide fire and intrusion protection. Intrusion-alarm systems can be combined with closed-circuit television (CCTV) systems to record intruders’ activities and interface to access control systems with electrically locked doors.

In addition to the system itself, security alarms can be linked to a monitoring service. In the event of an alarm, the premises control unit contacts a central monitoring station. Operators at the station see the signal and take appropriate action, such as contacting property owners, notifying police, or dispatching private security patrols. Such alerts transmit via dedicated alarm circuits, telephone lines, or by internet.

The trigger signal from every sensor is transmitted to one or more control units either through wires or wireless means. Wired systems are convenient when sensors (such as PIRs, smoke detectors, etc.) require external power to operate correctly, however, they may be more costly to install.

Wireless systems, on the other hand, use battery-powered transmitters which are easier to install and have less expensive start-up costs, but may fail if the batteries are not maintained. Depending on distance and construction materials, one or more wireless repeaters may be required to bring the signal to the alarm panel reliably.

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.)