alert status; emergency alert
advisory level; 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
special precautions; special vigilance
warning color; warning colour
warning signal; restricted speed signal
official warning (esp. of an impending earthquake)
special precautions; heightened vigilance