A burglar alarm, also known as a security alarm, security system, alarm system, or intrusion detection system, can be used in residential, commercial, or industrial settings to detect unauthorized entry into a building or area.

In the most basic form, a burglar alarm may consist of one or more sensors used to detect intruders, along with an alerting device to indicate the intrusion. More complex systems may also include closed-circuit television surveillance systems which automatically record the activities of intruders. In addition, burglar alarm systems may also be equipped with smoke, heat, and carbon monoxide detectors, protecting from additional risks.

Burglar alarms may be either local or remote, depending upon the application. Local alarms do not include monitoring, although may include indoor and outdoor sounders and lights. Remote alarms, commonly referred to as monitored alarms, will communicate an event such as an intrusion to a monitoring company, in addition to the use of localized sounders and lights.

Debating the merits of a monitored verses non-monitored alarm? The widespread use of alarm systems has desensitized many urbanites that tend to ignore alarms, never contacting the necessary authorities. In many cases, legitimate alarms receive no response. Alternatively, in rural areas, where neighbours may be quite a distance away, lights or sounds may not make a difference. It is entirely possible that nothing will be done to avoid potential losses.