Alerting

9 clues
Warning
Tipping off
Siren's function
Putting on guard
Red flag's purpose
Sounding the alarm
Giving a heads-up to
Emulating Paul Revere
Paul Revere's midnight duty
Similar answers:
Aaarating
Aameeting
Aameetings
Abating
Abbreviating
Abducting
Abetting
Ablastingindisguise
Aborting
Abtesting
Abutting
Accenting
Accentinganexam
Accepting
Accidentsarewaiting
Accommodating
Accosting
Accountingclerk
Accountingcrows
Accountingerror