Bell code
Bell codes or Buzzer codes are a series of bells or buzzers used on passenger trains for communication between the driver and guard.
Great Britain and India
All codes, except 3—2—1, must be acknowledged by repeating the code received.United States
In the United States, these are known as Communication Signal Appliance codes.| Signal | Meaning |
| _ | When running, stop at once. |
| _ | When standing, apply or release brakes. |
| o o | When standing, start. |
| o o o | When standing or running backward, back up two car lengths. |
| o o o | When running forward, stop at next passenger station. |
| o o o o | When standing, brakes have applied and released on rear car. Brake test completed. |
| o | When spotting, switching, or making up trains, prepare to stop. |