{{Short description|System to inform of a future danger}}
thumb|right|A HSS Engineering TWS 295 electronic sirens warning Civil Defense siren. [[File:Picswiss BL-56-08.jpg|thumb|There are 8,200 alarm sirens for civil protection throughout Switzerland. They are tested once a year, on the first Wednesday in February.<ref>[https://www.bevoelkerungsschutz.admin.ch/internet/bs/en/home/themen/alarmierung/sirenentest.html Testing sirens], Swiss Federal Office for Civil Protection (page visited on 7 September 2013).</ref> {{Audio|BABS - Allgemeiner Alarm.ogg|Sound sample}}]] [[Image:Laser Warning Light and Sign.jpg|thumb|Warning light indicating danger of laser exposure]]
A '''warning system''' is any system of biological or technical nature deployed by an individual or group to inform of a future danger. Its purpose is to enable the deployer of the warning system to prepare for the danger and act accordingly to mitigate or avoid it.{{how|date=June 2024}}{{citation needed|date=June 2024}}
Warnings cannot be effective unless people react to them. People are more likely to ignore a system that regularly produces false warnings (the cry-wolf effect), but reducing the number of false warnings generally also increases the risk of not giving a warning when it is needed.<ref>{{Cite journal| doi = 10.1016/j.ress.2015.05.003| issn = 0951-8320| volume = 142| pages = 192–202| last1 = Sättele| first1 = Martina| last2 = Bründl| first2 = Michael| last3 = Straub| first3 = Daniel| title = Reliability and effectiveness of early warning systems for natural hazards: Concept and application to debris flow warning| journal = Reliability Engineering & System Safety| access-date = 2018-02-07| date = October 2015| url = https://www.era.bgu.tum.de/fileadmin/w00bkd/www/Papers/2013_Saettele_et_al_Reliability_EWS.pdf| doi-access = free| archive-date = 2018-02-07| archive-url = https://web.archive.org/web/20180207122945/http://www.era.bgu.tum.de/fileadmin/w00bkd/www/Papers/2013_Saettele_et_al_Reliability_EWS.pdf| url-status = dead}}</ref> Some warnings are non-specific: for instance, the probability of an earthquake of a certain magnitude in a certain area over the next decade. Such warnings cannot be used to guide short-term precautions such as evacuation. Opportunities to take long-term precautions, such as better building codes and disaster preparedness, may be ignored.<ref>{{Cite web|url=https://www.theguardian.com/science/blog/2012/may/30/attempts-predict-earthquakes-harm-good|title = Attempts to predict earthquakes may do more harm than good | Professor David Petley|website = TheGuardian.com|date = 30 May 2012}}</ref>{{better citation needed|date=February 2018}} thumb|Early warning siren for earthquakes and floods
==Biological warning systems== *Aposematism (e.g. warning coloration) *Climate canary *Fear *Miner's canary *Pain
==Man-made warning systems== *Emergency population warning
===Civilian warning systems=== [[Image:Wheelock-as.jpg|thumb|A fire alarm that warns people if a building is on fire]]
* Alberta Emergency Alert * Alberta Emergency Public Warning System (replaced by Alberta Emergency Alert)<ref>[https://www.municipalaffairs.gov.ab.ca/ema_epws.htm] {{webarchive|url=https://web.archive.org/web/20061212051852/https://www.municipalaffairs.gov.ab.ca/ema_epws.htm|date=December 12, 2006}}</ref> * Alert Ready (Canada) * Automatic Warning System * Child abduction alert system * Dam safety system * Earthquake warning system * Emergency Alert System (EAS) (United States) * Famine Early Warning Systems Network * Federal Civil Defense Authority * Fire alarm system * Gale warning * Ground proximity warning system * Indian Ocean Tsunami Warning System * International Early Warning Programme * J-Alert (Japan) * Lane departure warning system * National Severe Weather Warning Service * N.E.A.R. (National Emergency Alarm Repeater) * North Warning System * Standard Emergency Warning Signal (Australia) * Traffic Collision Avoidance System * Train Protection & Warning System * Tsunami warning system
===Military warning systems=== Historical beacon-based systems: * Byzantine beacon system in Asia Minor during the 9th century
Space-based missile early warning systems: * Defense Support Program (United States, to be succeeded by the "Space-Based Infrared System") * Space-Based Infrared System (SBIRS) (United States) * Oko, also known as "SPRN" (Russia)
Airborne early warning systems: * Airborne Early Warning and Control ("AWACS" for NATO, many countries have developed their own AEW&C systems)
Ground-based early warning radar systems: * Ballistic Missile Early Warning System and PAVE PAWS (United States) * Duga radar, also known as the "Russian Woodpecker" (Russia) * Dnestr radar (1st generation Russian) * Daryal radar (2nd generation Russian) * Voronezh radar (3rd and current generation Russian) * Chain Home (British, now defunct) * Chain Home Low (British, now defunct) * ROTOR (British, now defunct)
Optical sensors: * Bomb Alarm System
Emergency broadcasting: * CONELRAD (United States, succeeded by the Emergency Broadcast System) * Emergency Broadcast System (EBS) (United States, succeeded by the Emergency Alert System)
==See also== *Alarm (disambiguation)
== Notes and references == {{commons category|Warning systems}} {{reflist}}
Category:Emergency communication Category:Warning systems