warning bell; first bell; preliminary bell
A bell that rings shortly before a formal start time, such as before a class, meeting, or work period, signaling that the main activity will begin soon. Often contrasted with 本鈴 (the main bell).
See also: 本鈴
The warning bell rang, so I hurried back to the classroom.
予鈴と本鈴の間は5分間です。
There is a five-minute interval between the warning bell and the main bell.