Bell codes, buzzer codes or Communication Signal Appliance codes entail a series of bells or buzzers used on passenger trains for communication between the driver and guard.
| Signal | Meaning in Great Britain[1] | Meaning in India[2] | |
|---|---|---|---|
| 1 | Stop | Stop train | |
| 1—1 | Zone of speed restriction over, resume prescribed speed | ||
| 1—2 | Close doors | ||
| 2 | Ready to start | Start train | |
| 2—2 | Do not open doors | Passing automatic signal at 'on' | |
| 3 | Set Back | Guard required by driver | |
| 3—1 | Lock central door locking | ||
| 3—2—1 | Testing doors | ||
| 3—3 | Guard required by driver, or guard or driver to speak on the telephone | Guard's warning when the motorman exceeds the speed prescribed | |
| 3—3—1 | Release central door locking | ||
| 4 | Slow down | Protect train in rear | |
| 5 | Driver/Guard leaving the train | ||
| 6 | Draw forward | ||
| 9 | Police assistance required |
All codes, except 3—2—1, must be acknowledged by repeating the code received.
In the United States, these are known as Communication Signal Appliance codes.
| Signal | Meaning[3] | |
|---|---|---|
| _ | 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. |