wake-up call
noun /ˈweɪk ʌp kɔːl/
  /ˈweɪk ʌp kɔːl/
 - a phone call that you arrange to be made to you at a particular time, for example in a hotel, in order to wake you up
- I asked for a wake-up call at 6.30 a.m.
 
 - an event that makes people realize that there is a problem that they need to do something about
- These riots should be a wake-up call for the government.