wake-up call

(noun) a warning to take action concerning something that was overlooked or neglected. Synonyms: wake-up call. Example: "The bombing was a wake-up call to strengthen domestic security."

(noun) a telephone call that you request be made a specific time in order to wake you up at that time (especially in hotels). Synonyms: wake-up call. Example: "She left a wake-up call for 7 a.m.."