A false alarm, also called a nuisance alarm, is the fake report of an emergency, causing unnecessary panic and/or bringing resources (such as emergency services) to a place where they are not needed. Over time, repeated false alarms in a certain area may cause occupants to start to ignore all alarms, knowing that each time it will probably be false. The concept of this can be traced at least as far back as Aesop's story of The Boy Who Cried Wolf, where many episodes of a boy falsely yelling "wolf" caused the townspeople to ignore his cries when a real wolf came. In addition, false alarms have the potential of diverting emergency responders away from legitimate emergencies, which could ultimately lead to loss of life.
In industrial alarm management, a false alarm could refer either to an alarm with little information content that can usually safely be eliminated, or one that could be valid but is triggered by a faulty instrument. Both types are problematic because of the "cry wolf" effect described above.
The term "false alarm" is actually a misnomer, and is regularly replaced by the term "nuisance alarm." When a sensor operates, it is hardly false, and it is usually a true indication of the present state of the sensor. A more appropriate term is nuisance, indicating that the alarm activation is inconvenient, annoying, or vexatious. A prime example of this difference is burglar alarms being set off by spiders. (A spider crawling on a web in front of the motion detector appears very large to the motion detector.) [1]
One tragic example of the consequences of continued false alarms was at Boland Hall at Seton Hall University on January 19, 2000. Months of false fire alarms caused many students to start ignoring the fire alarms. However when an actual fire broke out, three students who ignored the fire alarms died and many others suffered injuries.
Likewise, after too many audible car alarms are found false, most people no longer pay attention to see whether someone is stealing a vehicle, so even certain experienced thieves may confess that these alarms would not deter them from stealing vehicles.
Intentional false alarms of any kind, especially through emergency notification systems, are very serious criminal offenses, and can result in very severe legal punishments.
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In (signal) detection theory, a false alarm occurs where a non-target event exceeds the detection criterion and is identified as a target (see Constant false alarm rate).
False alarms could also refer to situations where one becomes startled about something that is later determined to be untrue.
Sometimes a package can set off a dectector if it contains almonds as they emit a similar odour to semtex.