wake-up call

1. A telephone call that one requests to occur at a specific time in order to be woken up, especially in a hotel.
2. A sign or warning that alerts one to negative or dangerous behavior or circumstances: "Her personal life was spiraling out of control . . . and her brush with death came as a wake-up call" (Geraldine Fabrikant).

A portentous event, report, or situation that brings an issue to immediate attention. For example, The rise in unemployment has given a wake-up call to state governments, or The success of the online subscription is a wake-up call to publishers. This metaphoric term originated in the second half of the 1900s for a telephone call arranged in advance to awaken a sleeper, especially in a hotel. Its figurative use dates from about 1990.