expression, godan verb (-ku)
notice; realize; become aware of
The most common use: to become aware of something through one's senses or intuition. Often followed by ～に気がつく or a clause with ～と/～ことに.
彼は自分の間違いに気がついた。
He noticed his own mistake.
外
I didn't realize it had gotten dark outside.
expression, godan verb (-ku)
be attentive; be observant; be scrupulous
Describes a person's character or habitual carefulness, often in the form 気がつく (person). Less common than sense 1.
彼女はとても気がつく人で、いつも細かいところまで見ている。
She is a very observant person and always pays attention to details.
expression, godan verb (-ku)
Used when someone recovers from fainting or a coma. Often in the form 気がついたら～ (when I came to...).
病院で気がついたとき、家族がそばにいた。
When I came to at the hospital, my family was by my side.