Synonyms:
unwary
Meaning: not alert to danger or deception; "the shrieks of unwary animals taken by surprise"; "some thieves prey especially on unwary travelers"; "seduce the unwary reader into easy acquiescence"- O.J.Campbell
Usage examples
The unwary footstep!
It was once upon a time the trick of a countryman to bring a Cat to market in a bag, and substitute it for a sucking pig in another bag, which he sold to the unwary when he got the chance.
All its length and breadth was paved with smooth bricks of a bright yellow color, so it was smooth and level except in a few places where the bricks had crumbled or been removed, leaving holes that might cause the unwary to stumble.