also: しらぬあいだに
expression
before one knows it; without noticing; unawares
Describes something happening or changing while one is unaware, often with a nuance of surprise or inevitability. Synonymous with 知らない間に.
See also: 知らない間に
知らぬ間に雨が降り出していた。
It had started raining before I knew it.
知らぬ間に彼は部屋を出て行った。
He left the room without my noticing.