1. figurative: something that alerts people to a problematic situation
heart attack was a wake-up call for him
A 'wake up call' is a telephone call made at an agreed time in order to wake someone up, usually in a hotel. A 'wake up call' is also an event or something that alerts someone to an unsatisfactory situation or a problem and gives them the opportunity to remedy it. This is a common noun used in both social and professional contexts.