Definition of alert verb from the Oxford Advanced Learner's Dictionary

alert

verb
əˈlɜːt
 
; əˈlɜːrt
 
 
[often passive]1 alert somebody (to do something)| alert somebody (that)… to warn somebody about a dangerous or urgent situationNeighbours quickly alerted the emergency services.Alerted by a noise downstairs, he sat up and turned on the light.2 alert somebody to something to make somebody aware of somethingThey had been alerted to the possibility of further price rises.