false alarm(n = noun.communication) - a warning that is given about something that fails to occur;
is a kind of warning

N  alarm, alarum, larum, alarm bell, tocsin, alerts, beat of drum, sound of trumpet, note of alarm, hue and cry, fire cross, signal of distress, blue lights, war-cry, war- whoop, warning, fogsignal, foghorn, yellow flag, danger signal, red light, red flag, fire bell, police whistle, false alarm, cry of wolf, bug-bear, bugaboo, alarming, Int, sauve qui peut!, every man for himself!, qui vive?.

alarm, alarm bell, alarm clock, alarm system, bearing false witness, blue false indigo, burglar alarm, california false morel, false, false alumroot, false asphodel, false azalea, false baby's breath, false beachdrops, false belief, false bittersweet, false bracken, false buckthorn, false bugbane, false calyx, false chamomile, false deathcap, false dogwood, false dragon head, false dragonhead, false face, false foxglove, false front, false fruit, false garlic, false gavial, false glottis, false goatsbeard, false gromwell, false hair, false heather, false hellebore, false imprisonment, false indigo, false labor, false lily of the valley, false lupine, false mallow, false mildew, false mistletoe, false miterwort, false mitrewort, false modesty, false morel, false move, false name, false nettle, false oat, false pimpernel, false pregnancy, false pretence, false pretense, false ragweed, false return, false rue, false rue anemone, false saber-toothed tiger, false saffron, false sago, false sarsaparilla, false scorpion, false show, false smut, false step, false tamarisk, false teeth, false topaz, false truffle, false vampire, false vampire bat, false verdict, false vocal cord, false vocal fold, false wintergreen, false witness, fire alarm, play false, red false mallow, saddled-shaped false morel, scentless false camomile, smoke alarm, sweet false chamomile, white false indigo