Meaning of 敏い in Japanese

さりげなく聡いこの子にはうかつな事はとても言えない。
You just can't let things slip around this nonchalantly smart girl.

彼は金もうけのあらゆる機会に目ざとい。
He is alert to every chance of making money.

年を取ると目ざとくなる。
As one grows old, one becomes a light sleeper.