heads up

1.気をつけろ！Watch outに近い表現
2.a heads-up: 一応警告、前もって言っておくけど

Ex

• 1.Heads up!!
• 2.If you see the boss coming, give me a heads-up.
• 2.Hey, I just want to give you a heads-up that the show starts in ten minutes.

Reference source

• https://talking-english.net/heads-up/
• https://www.us-lighthouse.com/study/english-lesson/heads-up.html