School bell
The ringing of a school bell announces important times to a school's students and staff, such as marking the beginnings and ends of the school day, class periods, and breaks.
Back in the day (and still today in some schools), it may take the form of a physical bell, usually electrically operated, while in most modern schools, it may be a tone, siren, electronic bell sound, a series of chimes, or music played over an intercom. In East Asian nations such as China, North Korea and South Korea, the Westminster Chimes pattern is commonly played as the bell, which is also used in some schools internationally.
Schools for the hearing impaired use alternative signaling methods, for example sign language from the teacher and lights that illuminate when the public address/bell is sounding.