This is a reminder but nothing happens after it! You can still eat and pray!

There were two calls for salaat ul-fajr (prayer the first just before dawn—for those who are awake performing night prayers so as for them to either rest for Fajr or have food if they intend to fast the next day, and for those who are asleep in order they may begin to arise and be ready for Fajr. Sheikh, it means after first call of adhan we should stop praying tahajud & take rest?