Expressions (phrases, clauses, etc.), Godan verb with 'ku' ending
to notice; to realize; to realise; to become aware (of); to perceive; to sense; to suspect
ドアを閉めてから、鍵を置いてきたことに気がついた。After I shut the door, I remembered I had left my key behind. to be attentive; to be scrupulous; to be observant
to regain consciousness; to come to (one's senses); to come round
Also written 気が付く【きがつく】