How to say "alert" in Japanese

• アラートCommon
  nounThe loanword noun for an alert: a warning or, especially, a state of vigilance, familiar from technical and security contexts — a thing or a state, not a personal quality.
• 敏感びんかんJLPT N1approx.Common
  na-adjective, nounEssentially 'sensitive': quick to react to stimuli, changes, or delicate matters. As 'alert' it only suggests keen awareness, so it is seldom the word you want for a warning or a state of vigilance.
  私は寒さむさに敏感びんかんだ。↗

  I am very sensitive to the cold.
• 警報けいほうCommon
  nounA warning or alarm — the noun for an alert officially issued or sounded about danger, as for storms or other emergencies; not a word for personal quickness.
  その警報けいほうで皆みな部屋へやから飛び出とびだした。↗

  The alarm sent everyone rushing out of the room.
• 機敏きびんCommon
  na-adjective, nounThe adjective 'alert' in the sense of quick and keen: a person, movement, or response that is prompt and nimble. It praises brisk, sharp action rather than naming any warning.
  警察けいさつは力ちからがあって、動作どうさが機敏きびんでなければならない。↗

  A policeman should be strong and quick in action.
• 素早いすばやいJLPT N1approx.Common
  i-adjectiveDescribes quickness of movement or of understanding and judgement. As 'alert' it means someone reacts or catches on fast; it does not refer to warnings or alarms.
  彼かれは素早すばやくフランス語ふらんすごを習得しゅうとくした。↗

  He acquired French quickly.

For the warning sense use the nouns 「アラート」 or 警報; for the adjective 'alert' meaning quick and keen in response use 機敏 or 「素早い」; 敏感 is really 'sensitive' and only marginally 'alert'.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

• アラートalert
• 敏感びんかんsensitive
• 警報けいほうwarning
• 機敏きびんquick
• 注意を喚起するちゅういをかんきするto alert
• 注意喚起ちゅういかんきcall for attention
• 抜け目ないぬけめないshrewd
• 抜け目のないぬけめのないshrewd
• 抜け目がないぬけめがないshrewd
• 警急けいきゅうalarm
• 素早いすばやいquick (understanding, judgement, etc.)
• 敏捷びんしょうquick (thinking)