The doorkeeper gave the alarm as soon as he saw the smoke.守门人一看见冒烟就发出警报。When he realized that one engine was not working, the pilot alerted air traffic control.当飞行员注意到一台发动机失灵，便向空中交通指挥部发出警报。Sound the alarm.发出警报。They rang the bells to sound the alert.他们敲响了钟，发出警报。