Alarm

Alarms are used in a variety of places to give warning of a problem. The commonest are burglar alarms, designed to warn of intrusions, and safety alarms, which go off if a dangerous condition occurs. Common public safety alarms include tornado sirens and fire alarms. See also air raid siren. Alarms, from innocuous sirens to actual smoke detectors, have the capability of causing a fight or flight response in humans; a person under this mindset will panic and either flee the perceived danger or attempt to eliminate it, often ignoring rational thought in either case.

With any kind of alarm, there is a need to balance between the danger of false alarms (called a false positive) -- the signal going off in the absence of a problem -- and failing to signal an actual problem (called a false negative). False alarms can be expensive to respond to, and even dangerous. For example, false alarms of a fire can waste firefighter manpower, making them unavailable for a real fire, and risk injury to firefighters and others as the fire engines race to the location where there is believed to be a fire. In addition, false alarms lead people to ignore the alarm signal, and thus possibly to ignore an actual emergency: this is the lesson of Aesop's fable of The Boy Who Cried Wolf.

Alarms are generated by distributed control manufacturing systems or DCS's found in nucleur power plants, refineries and chemical facilities. See Alarm management.