Is this normal? For my mom

My mom sleeps throughout the day usually when I come home from school she naps, but the weird thing is She is always awakend by the sound of a doorbell which keeps waking her up I don't know if it happens at night because she doesn't call me or anything but for the past week whenever I come home from school and she tries to nap she keeps waking up to the sound of the doorbell being rung does anybody know what this is???