get http://{localIP}/light/warning_beep
The warning beep is implemeneted as a light in ESPHome so that built-in strobe effects can be used to make a repeating beep. In reality it's not actually a light. This endpoint simply controls an output that can be attached to a buzzer, sounder or light.
By default, on the 6-zone Alarm Panels, the warning beep output is the same as the ALRM or OUT switched output. On the Alarm Panel Pro, OUT1 is used as the warning beep output.