Buzzer

The flight controller's buzzer tells you what it's doing without a screen: calibration done, arming, battery warnings, lost link. Choose which events sound on the Beepers tab, or with the beeper command.

What the beeps mean

Sound	Event	Meaning
3 short beeps after power-up	GYRO_CALIBRATED	Gyro calibration finished. Keep the helicopter still until you hear it -- moving it restarts the calibration.
One long beep then a short one	ARMING	Armed.
Two medium beeps	DISARMING	Disarmed.
Short beep every 2.5 s	ARMED	Reminder that the flight controller is armed.
Repeating beep, 0.5 s on / 0.5 s off	RX_LOST	No signal from the receiver.
SOS in Morse	RX_LOST_LANDING	Failsafe active.
Repeating beep, 0.25 s on / 0.5 s off	BAT_LOW	Battery at the warning level.
Almost continuous tone	BAT_CRIT_LOW	Battery critically low.
Short beep, on demand	RX_SET	The BEEPER mode switch -- for finding a crashed helicopter.
Two short beeps	ACC_CALIBRATION / BLACKBOX_ERASE	Accelerometer calibration or Blackbox erase finished.
Two longer beeps	ACC_CALIBRATION_FAIL	Accelerometer calibration failed.
Melody	READY_BEEP	Ready (with GPS: fix acquired).
Counted beeps	GPS_STATUS / MULTI_BEEPS	Satellite count, or a confirmation -- e.g. one beep per in-flight adjustment, and the profile number when switching PID profile.
--	ON_USB	Allows beeping while powered from USB only. Usually off.

The beeper command

beeper                  # list which events are on
beeper -<EVENT>         # turn an event off, e.g. beeper -ON_USB
beeper <EVENT>          # turn it on again

play_sound [n] plays the sounds in turn (or sound n) -- handy to hear them on the bench.

DShot beacon

With DShot ESCs, the motor can beep too (beacon command, and the ESC Beacon section of the Beepers tab) -- for finding a helicopter in long grass after a crash. beeper_dshot_beacon_tone sets the tone. It can't sound while the motor runs, and arming waits two seconds after the last beacon tone.

Buzzer hardware

The buzzer output switches a pin on and off, so it needs an active buzzer -- one that makes its own tone when powered. Passive buzzers that need a PWM signal only click. Rotorflight flight controllers have one built in, or a buzzer header.

On the bench, a buzzer powered from the servo rail only works if that rail is powered.