wake-up_call
1. [ noun ] a warning to take action concerning something that was overlooked or neglected
Examples:

"the bombing was a wake-up call to strengthene domestic security"

Related terms: warning
2. [ noun ] (telecommunications) a telephone call that you request be made a specific time in order to wake you up at that time (especially in hotels)
Examples:

"she left a wake-up call for 7 a.m."

Related terms: call
Similar spelling:   wake-up_signal