To notice or become aware of something; to perceive or realize a fact or change.
駅に着いてから財布を忘れたことに気がついた。
I realized I'd forgotten my wallet after arriving at the station.
彼女は髪型が変わったことにすぐ気がついた。
She immediately noticed the change in her hairstyle.
匂いで料理が焦げていることに気がついた。
I noticed by the smell that the food was burning.
To be attentive or observant; to notice small details and be careful or scrupulous.
彼は細かい変化にもすぐ気がつくタイプだ。
He's the type who notices even small changes right away.
看護師は患者の小さな変化にも気がつかなければならない。
Nurses must be attentive to even small changes in patients.
To regain consciousness or come to one's senses; used when someone wakes up or recovers awareness.
倒れていたが、しばらくして気がついた。
He had collapsed, but after a while he came to.
手術後、患者がゆっくりと気がつき始めた。
After the operation, the patient slowly began to regain consciousness.