Vigilance or caution — being on guard and taking precautions against danger or problems; alertness to prevent harm.
夜道では常に警戒を怠らないでください。
Don't let your guard down on streets at night.
洪水の危険があるため、住民に警戒を呼びかけた。
Because of the flood risk, residents were urged to be on alert.
警戒レベルが引き上げられたので外出を控えた。
Because the alert level was raised, I refrained from going out.