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Cleanflight supports a buzzer which is used for the following purposes:
* Low and critical battery alarms (when battery monitoring enabled)
* Arm/disarm tones (and warning beeps while armed)
* Notification of calibration complete status
* TX-AUX operated beeping - useful for locating your aircraft after a crash
* Failsafe status
* Flight mode change
* Rate profile change (via TX-AUX switch)
If the arm/disarm is via the control stick, holding the stick in the disarm position will sound a repeating tone. This can be used as a lost-model locator.
Three beeps immediately after powering the board means that the gyroscope calibration has completed successfully. Cleanflight calibrates the gyro automatically upon every power-up. It is important that the copter stay still on the ground until the three beeps sound, so that gyro calibration isn't thrown off. If you move the copter significantly during calibration, Cleanflight will detect this, and will automatically re-start the calibration once the copter is still again. This will delay the "three beeps" tone. If you move the copter just a little bit, the gyro calibration may be incorrect, and the copter may not fly correctly. In this case, the gyro calibration can be performed manually via [stick command](Controls.md), or you may simply power cycle the board.
There is a special arming tone used if a GPS fix has been attained, and there's a "ready" tone sounded after a GPS fix has been attained (only happens once). The tone sounded via the TX-AUX-switch will count out the number of satellites (if GPS fix).
The CLI command `play_sound` is useful for demonstrating the buzzer tones. Repeatedly entering the command will play the various tones in turn. Entering the command with a numeric-index parameter (see below) will play the associated tone.