Answered by Shaykh Yusuf Weltch
In our neighborhood, a few minutes before fajr azan, a siren sounds to signal the end of sehri. I believe the siren occurs before Subh Sadiq. But last year, after the siren, I was drinking water when Azan began, and I don’t remember if I had water in my mouth, and if I did, did I spit it or drink it. If I spat it, do I need to make up that fast in this case, and do I also need to make kaffarah if I drank the water when azan began?
In the Name of Allah, the Most Merciful and Compassionate
You are not required to make up the fast of the day in question for the following reasons:
The basis is that the night remains. An assumption to the contrary is only recognized if you are reasonably sure or certain that the Fajr time (Subh Sadiq) entered. [Ibn Nujaym, al-Ashbah wal-Nazair]
In the case that you described, the evidence leans to the Fajr time not entering. You mentioned that the siren was called prior to the entrance of the Fajr time (Subh Sadiq).
It is recommended for you to stop drinking and eating before the occurrence of any possible doubt whether the Fajr time has entered. Others schools strongly encourage abstaining from food and drink 15 minutes before the entrance of Fajr.
Hope this helps
Allah knows best
[Shaykh] Yusuf Weltch
Checked and Approved by Shaykh Faraz Rabbani