wake-up call

noun2

1. •
   A telephone call to awaken someone at a certain time, especially one requested by the person while staying at a hotel.

   • She requested a five a.m. wake-up call from the front desk.
2. •
   (figurative) An alert, reminder, or call to action caused by a dramatic event.

   • The recent deaths should serve as a wake-up call to others at risk.