Use 'watch out' to quickly alert someone to immediate danger or a hazard.

Urgent Warning

'Watch out' is typically used in casual or informal speech rather than formal situations.

Colloquial Use

'Watch out' often stands alone as an exclamation, especially in urgent situations.

When watching out for someone or something, it means to be continuously observant.

Use it when there is a potential for harm or a problem, not necessarily immediate.

Implies caring for and protecting something or someone from potential problems.