alert status; emergency alert
advisory level (1-5, 5 being the most severe); warning level
sense of caution; wariness
preliminary alert (flood, typhoon, air-raid, etc.); precautionary warning
warning line; police cordon
hazard area (flood, tsunami, etc.); danger zone; no man's land
warning color; warning colour
special precautions; special vigilance
full alert; special watch
high alert; severe warning
warning signal; restricted speed signal
official warning (esp. of an impending earthquake)
alert level; warning level
special precautions; heightened vigilance
cordon (e.g. police, military)