what is the signifiance of the ararm clock by Mrs. Dubose bed? what does scout suddenly notice about it one day?

As time passes, the old woman stops speaking and her mouth opens and closes while her head sways from side to side. Jem asks her if she is all right, but she doesn't reply. In a few minutes, an alarm clock sounds, and Mrs. Dubose's assistant shoes them out of the room and tells them to go home because it is time for Mrs. Dubose's medicine. The Alarm clock signals the old lady's morphine time.