Thank you for reaching us!
I understand that you would like to get the alert when the service account is login to achieve this, you’ll need to export sign-in logs to a Log Analytics workspace, then set up the triggers.
For more information you can refer the below article
Receive an alert on user login – Azure AD
Hope this helps. Do let us know if you any further queries.
Thanks,
Akhilesh.
If this answers your query, do click Accept Answer
and Yes
for was this answer helpful. And, if you have any further query do let us know.