Warning system


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.
Warnings cannot be effective unless people react to them. People are more likely to ignore a system that regularly produces false warnings, but reducing the number of false warnings generally also increases the risk of not giving a warning when it is needed. 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.

Biological warning systems

Man-made warning systems

Civilian warning systems

Image:Wheelock-as.jpg|thumb|A fire alarm that warns people if a building is on fire

Military warning systems

Historical beacon-based systems:
Space-based missile early warning systems:
Airborne early warning systems:
Ground-based early warning radar systems:
Optical sensors:
Emergency broadcasting: