Alerting but not if you start in first gear (9)
I believe the answer is:
'alerting' is the definition.
The answer and definition can be both related to communication as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'not if you start in first gear' is the wordplay.
'you start' becomes 'y' (I've seen this in other clues).
'first gear' becomes 'g' (1st letter of 'gear').
'but' acts as a link.
Can you help me to learn more?
(Another definition for notifying that I've seen is " Officially informing (someone)".)