1
general::
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.
American Heritage Idioms