All Clear

everything is OK, the danger has passed, signal that the situation is safe

All Clear is a term used by civil defense or military authorities to inform others that an imminent physical danger has passed. This typically will end an alert or warning status that was previously issued. The All Clear can be given vocally, through media – such as television or radio, or via means of civil defense broadcast systems such as air raid and storm sirens.
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Noun
1. a signal (usually a siren) that danger is over
(hypernym) signal, signaling, sign
2. permission to proceed because obstacles have been removed
(hypernym) permission

Term used in boating to mean 1) That a tow boat is ready to leave barge or 2) Is clear of an obstruction. (TNDOT1)

Synonyms and related words:
Klaxon, Mayday, SOS, above water, air-raid alarm, alarm, alarm bell, alarm clock, alarm signal, alarum, alert, all straight, beacon, blinking light, burglar alarm, buzzer, clear, crostarie, fiery cross, fire alarm, fire bell, fire flag, five-minute gun, flashing light, fog bell, fog signal, foghorn, free and clear, gale warning, hooter, horn, hue and cry, hurricane warning, lighthouse, note of alarm, occulting light, out of debt, police whistle, signal of distress, siren, small-craft warning, solvent, still alarm, storm cone, storm flag, storm warning, tocsin, two-minute gun, unindebted, unowing, upside-down flag, whistle,