Security Alarms

An alarm gives an audible or visual warning of a problem or condition. 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. We can characterise a person in such a state as "alarmed".

With any kind of alarm, the need exists to balance between on the one hand the danger of false alarms (called "false positives") — the signal going off in the absence of a problem — and on the other hand failing to signal an actual problem (called a "false negative"). False alarms can waste resources expensively 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 alleged fire's location. In addition, false alarms may acclimatise people to ignore alarm signals, and thus possibly to ignore an actual emergency: Aesop's fable of The Boy Who Cried Wolf exemplifies this problem.

Burglar Alarm

Burglar (or intrusion), fire and safety alarms are found in electronic form today. Sensors are connected to a control unit via either a low-voltage hardwire or narrowband RF signal, which in turn connects to a means for announcing the alarm, hopefully to elicit some response. The most common security sensors indicate the opening of a door or window or detect motion via passive infrared (PIR). In new contruction systems are predominately hardwired for economy while in retrofits wireless systems may be more economical and certainly quicker to install. Some systems are dedicated to one mission, others handle fire, intrusion, and safety alarms simultaneously. Sophistication ranges from small, self-contained noisemakers, to complicated, multi-zoned digital systems with color-coded computer monitor outputs.