A false alarm is a warning or alert that turns out to be incorrect, untrue or mistaken. It can refer to any situation where an error has been made in identifying a threat or danger, leading people to believe there was a problem when in fact there wasn't one. For example, if the fire alarm goes off accidentally and there is no actual fire, it would be considered a false alarm. The phrase "false alarm" can also refer to situations where something appears to be serious or dangerous but turns out not to be, such as an illness that is initially thought to be life-threatening but later proves to be harmless.